The origins of the conflict lie in the complex nationality situation in Galicia at the turn of the 20th century. As a result of its relative leniency toward national minorities, the House of Habsburg (see: Austria-Hungary) was the perfect ground for the development of both Polish and Ukrainian national movements. During the 1848 revolution, the Austrians, concerned by Polish demands for greater autonomy within the province, gave support to a small group of Ruthenians (the name of the East Slavic people who would later adopt the self-identification of "Ukrainians" or "Rusyns") whose goal was to be recognized as a distinct nationality. After that, Ruthenian language schools were established, Ruthenian political parties formed, and the Ruthenians began attempts to develop their national culture. This came as a surprise to Poles, who until the revolution believed, along with most of the politically aware Ruthenians, that Ruthenians were part of the Polish nation (which, at that time, was defined in political rather than ethnographic terms). In the late 1890s and the first decades of the next century, the populist Ruthenian intelligentsia adopted the term Ukrainians to describe their nationality. Beginning with the 20th century, national consciousness reached a large number of Ruthenian peasants.
Multiple incidents between the two nations occurred throughout the latter 19th century and early 20th century. For example, in 1897 the Polish administration opposed the Ukrainians in parliamentary elections. Another conflict developed in the years 1901–1908 around Lviv University, where Ukrainian students demanded a separate Ukrainian university, while Polish students and faculty attempted to suppress the movement. In 1903 both Poles and Ukrainians held separate conferences in Lviv (the Poles in May and Ukrainians in August). Afterwards, the two national movements developed with contradictory goals, leading towards the later clash.
The ethnic composition of Galicia underlay the conflict between the Poles and Ukrainians there. The Austrian province of Galicia consisted of territory seized from Poland in 1772, during the first partition. This land, which included territory of historical importance to Poland, including the ancient capital of Kraków, had a majority Polish population, although the eastern part of Galicia included the heartland of the historic territory of Galicia-Volhynia and had a Ukrainian majority. In eastern Galicia, Ukrainians made up approximately 65% of the population while Poles made up only 22% of the population. Of the 44 administrative divisions of Austrian eastern Galicia, Lviv (Polish: Lwów, German: Lemberg), the biggest and capital city of the province, was the only one in which Poles made up a majority of the population. In Lviv, the population in 1910 was approximately 60% Polish and 17% Ukrainian. This city with its Polish inhabitants was considered by many Poles to have been one of Poland's cultural capitals. For many Poles, including Lviv's Polish population, it was unthinkable that their city should not be under Polish control.
The religious and ethnic divisions corresponded to social stratification. Galicia's leading social class were Polish nobles or descendants of Rus' gentry who had become polonized in the past, whereas, in the eastern part of the province Ruthenians (Ukrainians) constituted the majority of the peasant population. Poles and Jews were responsible for most of the commercial and industrial development in Galicia in the late 19th century.
Throughout the 19th and early 20th centuries the local Ukrainians attempted to persuade the Austrians to divide Galicia into Western (Polish) and Eastern (Ukrainian) provinces. These efforts were resisted and thwarted by those local Poles who feared losing control of Lviv and East Galicia. The Austrians eventually agreed in principle to divide the province of Galicia; in October 1916 the Austrian Emperor Karl I promised to do so once the war had ended.
Due to the intervention of Archduke Wilhelm of Austria, who adopted a Ukrainian identity and considered himself a Ukrainian patriot, in October 1918 two regiments of mostly Ukrainian troops were garrisoned in Lemberg (modern Lviv). As the Austro-Hungarian government collapsed, on October 18, 1918, the Ukrainian National Council (Rada), consisting of Ukrainian members of the Austrian parliament and regional Galician and Bukovynan diets as well as leaders of Ukrainian political parties, was formed. The Council announced the intention to unite the West Ukrainian lands into a single state. As the Poles were taking their own steps to take over Lviv and Eastern Galicia, Captain Dmytro Vitovsky of the Sich Riflemen led the group of young Ukrainian officers in a decisive action and during the night of October 31 – November 1, the Ukrainian military units took control over Lviv. The West Ukrainian People's Republic was proclaimed on November 1, 1918 with Lviv as its capital.
The timing of proclamation of the Republic caught the Polish ethnic population and administration by surprise. The new Ukrainian Republic claimed sovereignty over Eastern Galicia, including the Carpathians up to the city of Nowy Sącz in the West, as well as Volhynia, Carpathian Ruthenia and Bukovina (the last two territories were claimed also by Hungary and Romania respectively. Although the majority of the population of the Western-Ukrainian People's Republic were Ukrainians, many urban settlements had Polish majorities. In Lviv the Ukrainian residents enthusiastically supported the proclamation, the city's significant Jewish minority accepted or remained neutral towards the Ukrainian proclamation, while the city's Polish majority was shocked to find themselves in a proclaimed Ukrainian state. Because the West Ukrainian People's Republic was not internationally recognized and Poland's boundaries had not yet been defined, the issue of ownership of the disputed territory was reduced to a question of military control.
Fighting between Ukrainian and Polish forces was concentrated around the declared Ukrainian capital of Lviv and the approaches to that city. In Lviv, the Ukrainian forces were opposed by local self-defence units formed mostly of World War I veterans, students and children. However, skillful command, good tactics and high morale allowed Poles to resist the badly planned Ukrainian attacks. In addition, the Poles were able to skillfully buy time and wait for reinforcements through the arrangement of cease-fires with the Ukrainians. While Poles could count on widespread support from the civilian population, the Ukrainian side was largely dependent on help from outside the city. Other uprisings against Ukrainian rule erupted in Drohobych, Przemyśl, Sambir and Jarosław. In Przemyśl, local Ukrainian soldiers quickly dispersed to their homes and Poles seized the bridges over the River San and the railroad to Lviv, enabling the Polish forces in that city to obtain significant reinforcements.
After two weeks of heavy fighting within Lviv, an armed unit under the command of Lt. Colonel Michał Karaszewicz-Tokarzewski of the renascent Polish Army broke through the Ukrainian siege on November 21 and arrived in the city. The Ukrainians were repelled. Immediately after capturing the city, elements of the Polish forces as well as common criminals looted the Jewish and Ukrainian quarters of the city, killing approximately 340 civilians. The Poles also interned a number of Ukrainian activists in detention camps. The Ukrainian government provided financial assistance to the Jewish victims of the violence and were able to recruit a Jewish battalion into their army. Some factions blame these atrocities on the Blue Army of General Haller. This is unlikely as this French trained and supported fighting force did not leave France and the Western Front until April 1919, well after the rioting.
On November 9 Polish forces attempted to seize the Drohobych oil fields by surprise but, outnumbered by the Ukrainians, they were driven back. The Ukrainians would retain control over the oil fields until May 1919.
On November 11–12 Romanian troops seized Northern Bucovina without any resistance.
By the end of November 1918, Polish forces controlled Lviv and the railroad linking Lviv to central Poland through Przemyśl, while Ukrainians controlled the rest of Eastern Galicia east of the river San, including the areas south and north of the railroad into Lviv. Lviv thus faced Ukrainian forces on three sides.
In December 1918 fighting started in Volhynia with Polish troops invading the territory of Ukrainian People's Republic. As Polish units tried to seize control of the region, the forces of the Ukrainian People's Republic under Symon Petlura tried to recover the territory of Kholm Governorate already controlled by the Polish troops.
According to Richard Pipes, the first major pogrom in this region took place in January 1919 in the town of Ovruch, where Jews were robbed and killed by regiments affiliated with Symon Petlura's Cossack ataman, Kozyr-Zyrka. Nicolas Werth claims that armed units of the Ukrainian People's Republic were also responsible for rapes, looting, and massacres in Zhytomir, in which 500–700 Jews lost their lives.
After two months of heavy fighting the conflict was resolved in March 1919 by fresh and well-equipped Polish units under General Edward Rydz-Śmigły.
Thanks to fast and effective mobilization in December 1918, the Ukrainians possessed a large numerical advantage until February 1919, and pushed the Poles into defensive positions. According to an American report from the period of January 13 – February 1, 1919, Ukrainians eventually managed to surround Lviv on three sides. The city's inhabitants were deprived of water supply and electricity. Ukrainian army also held villages on both sidelines of the railway leading to Przemyśl.
Ukrainian forces continued to control most of eastern Galicia and were a threat to Lviv itself until May 1919. During this time, according to Italian and Polish reports, Ukrainian forces enjoyed high morale (an Italian observer behind Galician lines stated that the Ukrainians were fighting with the "courage of the doomed") while many of the Polish soldiers, particularly from what had been Congress Poland, wanted to return home because they saw no reason to fight against Ruthenians over Ruthenian lands; the Polish forces were outnumbered by two to one and lacked ammunition. Despite being initially outnumbered, the Poles had certain advantages. Their forces had many more and better trained officers resulting in a better disciplined and more mobile force; the Poles also enjoyed excellent intelligence and, due to their control of railroads behind their lines, were able to move their soldiers quite quickly. As a result, although the Poles had fewer total troops than did the Ukrainians, in particularly important battles they were able to bring in as many soldiers as did the Ukrainians.
On December 9, 1918 Ukrainian forces broke through the outer defences of Przemyśl in the hope of capturing the city and thus cutting off Polish-controlled Lviv from central Poland. However, the Poles were able to quickly send relief troops and by December 17 the Ukrainians were forced back. On December 27, bolstered by peasant troops sent to Galicia from Eastern Ukraine in the hopes that the Western Ukrainians would be able to form a disciplined force out of them, a general Ukrainian offensive against Lviv began. Lviv's defences held, and the eastern Ukrainian troops mutinied.
From January 6-January 11, 1919 a Polish attack by 5,000 newly recruited forces from formerly Russian Poland commanded by Jan Romer was repulsed by Western Ukrainian forces near Rava-Ruska, north of Lviv. Only a small number of troops together with Romer were able to break through to Lviv after suffering heavy losses. Between January 11 and January 13, Polish forces attempted to dislodge Ukrainian troops besieging Lviv from the south while at the same time Ukrainian troops attempted another general assault on Lviv. Both efforts failed. In February 1919, Polish troops attempting to capture Sambir were defeated by the Ukrainian defenders with heavy losses, although the poor mobility of the Ukrainian troops prevented them from taking advantage of this victory.
On February 14, Ukrainian forces began another assault on Lviv. By February 20, they were able to successfully cut off the rail links between Lviv and Przmysl, leaving Lviv surrounded and the Ukrainian forces in a good position to take the city. However, a French-led mission from the Entente arrived at the Ukrainian headquarters in February 22 and demanded that the Ukrainian cease hostilities under threat of breaking all diplomatic ties between the Entente and the Ukrainian government. On February 25 the Ukrainian military suspended its offensive. The Barthélemy (Marie Joseph Barthélemy|) mission proposed a demarcation line (February 28) leaving almost 70% of the East Galician territory to Ukrainians, and Lviv with oil fields to Poland. The Ukrainians would be supplied with half of the oil production. The proposal was accepted by the Poles. The Allied demands, which included the loss of significant amount of Ukrainian-held and inhabited territory, were however deemed to excessively favor the Poles by the Ukrainians, who resumed their offensive on March 4. On March 5 Ukrainian artillery blew up the Polish forces' ammunition dump in Lviv; the resultant explosion caused a panic among Polish forces. The Ukrainians, however, failed to take advantage of this. During the time of the cease fire, the Poles had been able to organize a relief force of 8,000–10,000 troops which by March 12 reached Przemyśl and by March 18 had driven the Ukrainian forces from the Lviv-Przmysl railroad, permanently securing Lviv.
On January 6–11 of 1919 a small part of the Ukrainian Galician Army invaded Transcarpathia to spread pro-Ukrainian sentiments among residents (the region was occupied by Hungarians and Czechoslovaks). Ukrainian troops fought with Czechoslovak and Hungarian local police. They succeeded in capturing some Hungarian-controlled Ukrainian settlements. After some clashes with Czechoslovaks, the Ukrainians retreated because Czechoslovakia (instead of Ukrainian People's Republic) was the only country that traded with the Western Ukrainian People's Republic and that supported it politically. Further conflict with the Czechoslovak authorities would have led to the complete economical and political isolation of the Western Ukrainian People's Republic.
on May 14, 1919, a Polish general offensive began throughout Volhynia and Eastern Galicia. It was carried out by units of the Polish Army aided by the newly arrived Blue Army of General Józef Haller de Hallenburg. This army, composed of Polish forces which had fought for the Entente on the Western front, numbering 60,000 troops, was well equipped by the Western allies and partially staffed with experienced French officers specifically in order to fight the Bolsheviks and not the forces of the Western Ukrainian People's Republic. Despite this, the Poles dispatched Haller's army against the Ukrainians in order to break the stalemate in eastern Galicia. The allies sent several telegrams ordering the Poles to halt their offensive as using of the French-equipped army against the Ukrainian specifically contradicted the conditions of the French help, but these were ignored, with the Polish side assessing that Ukrainians were Bolshevik sympathizers. At the same time, on May 23 Romania opened a second front against Ukrainian forces, demanding their withdrawal from the southern sections of eastern Galicia including from the temporary capital of Stanislaviv. This resulted in a loss of territory, ammunition and further isolation from the outside world.
The Ukrainian lines were broken, mostly due to the withdrawal of the elite Sich Riflemen. On May 27 the Polish forces reached the Złota Lipa–Berezhany-pl:Jezierna-Radziwiłłów line. The Polish advance was accompanied by a large wave of anti-Jewish violence and looting conducted not only by disorganized Polish mobs, as in Lviv in 1918, but by Polish military units operating against the orders of their officers, in particular those of the Poznań regiments and Haller's army. Following the demands of the Entente, the Polish offensive was halted and the troops of General Haller adopted defensive positions.
On June 8, 1919, the Ukrainian forces under the new command of Oleksander Hrekov, a former general in the Russian army, started a counter-offensive, and after three weeks advanced to Hnyla Lypa and the upper Stryi river, defeating five Polish divisions. Although the Polish forces had been forced to withdraw, they were able to prevent their forces from collapsing and avoided being encircled and captured. Thus, in spite of their victories, the Ukrainian forces were unable to obtain significant amounts of arms and ammunition. By June 27 the Ukrainian forces had advanced 120 km. along the Dnister river and on another they had advanced 150 km, past the town of Brody. They came to within two days' march of Lviv.
The successful Chortkiv offensive halted primarily because of a lack of arms – there were only 5–10 bullets for each Ukrainian soldier. The West Ukrainian government controlled the Drohobych oil fields with which it planned to purchase arms for the struggle, but for political and diplomatic reasons weapons and ammunition could only be sent to Ukraine through Czechoslovakia. Although the Ukrainian forces managed to push the Poles back approximately 120–150 km. they failed to secure a route to Czechoslovakia. This meant that they were unable to replenish their supply of arms and ammunition, and the resulting lack of supplies forced Hrekov to end his campaign.
Józef Piłsudski assumed the command of the Polish forces on June 27 and started yet another offensive, helped by two fresh Polish divisions. On June 28, the Polish offensive began. Short of ammunition and facing an enemy now twice its size, the Ukrainians were pushed back to the line of the river Zbruch by mid-July 1919. Although the Ukrainian infantry had run out of ammunition, its artillery had not. This provided the Ukrainian forces with cover for an orderly retreat. Approximately 100,000 civilian refugees and 60,000 troops, 20,000 of whom were combat ready, were able to escape across the Zbruch River into Eastern Ukraine.
The Polish and Ukrainian forces struggled on the diplomatic as well as military fronts both during and after the war. The Ukrainians hoped that the western allies of World War I would support their cause because the Treaty of Versailles that ended the first world war was based on the principle of national self-determination. Accordingly, the diplomats of the West Ukrainian People's Republic hoped that the West would compel Poland to withdraw from territories with a Ukrainian demographic majority.
Opinion among the allies was divided. Britain, under the leadership of prime minister David Lloyd George, and to a lesser extent Italy were opposed to Polish expansion. Their representatives maintained that granting the territory of the Western Ukrainian People's Republic to Poland would violate the principle of national self-determination and that hostile national minorities would undermine the Polish state. In reality, the British policy was dictated by unwillingness to harm Russian interests in the region and alienate the future Russian state through preventing possible union of Eastern Galicia with Russia. In addition, Britain was interested in Western Ukraine's oil fields. Czechoslovakia, itself involved in a conflict with Poland, was friendly towards the Ukrainian government and sold it weapons in exchange for oil. France, on the other hand, strongly supported Poland in the conflict. The French hoped that a large, powerful Polish state would serve as a counterbalance to Germany and would isolate Germany from Soviet Russia. French diplomats consistently supported Polish claims to territories also claimed by Germany, Lithuania and Ukraine. France also provided large numbers of arms and ammunition, and French officers, most notably General Haller's forces, to Polish forces that were used against the western Ukrainian military, much to the horror of Lloyd George and President Wilson.
The successful defence by the Ukrainian Galician Army of most of the West Ukrainian People's Republic territory in winter 1918–1919 prompted a diplomatic offensive by the Poles which sought to portray Ukrainian forces as Bolshevik, pro-German, or both, and which claimed that Ukrainians were illiterate, anarchic and unable to administer their own state. Polish diplomats declared that Ukrainians "were very ripe for Bolshevism, because they are very much under German influence ... and the Ukrainian people are led by a gang very similar to the Bolshevists ..."
In attempt to end the war, in January 1919 an Allied commission led by a French general was sent to negotiate a peace treaty between the two sides, prompting a ceasefire. In February it recommended that the West Ukrainian People's Republic surrender a third of its territory, including the city of Lviv and the Drohobych oil fields. The Ukrainians refused, the truce did not correspond to ethnology of the country or the military situation and broke diplomatic ties with Poland. In mid-March 1919, the French marshal Ferdinand Foch, who wanted to use Poland as an operational base for an offensive against the Red Army, brought the issue of Polish–Ukrainian war before the Supreme Council and appealed for large-scale Polish-Romanian military operation which would be conducted with Allied support, as well as sending Haller's divisions to Poland immediately to relieve Lviv from Ukrainian siege.
Another Allied commission, led by South African General Louis Botha, proposed an armistice in May that would involve the (West) Ukrainians keeping the Drohobych oil fields and the Poles keeping Lviv. The Ukrainian side agreed to this proposal but it was rejected by the Poles on the grounds that it didn't take into consideration the overall military situation of Poland and the circumstances on the eastern front. The Bolshevik army broke through the UNR forces and was advancing to Podolia and Volhynia. The Poles argued that they need military control over whole Eastern Galicia to secure the Russian front in its southern part and strengthen it by a junction with Romania. The Poles launched an attack soon afterward using a large force equipped by France (Haller's Army), which captured most of the territory of the West Ukrainian People's Republic. Urgent telegrams by the Western allies to halt this offensive were ignored. In late June 1919, the Allied Council approved the resolution allowing the Polish army (including Haller's troops) to advance through Eastern Galicia to the River Zbruch. Czechoslovakia, which had inherited seven oil refinaries from prewar Austrian times and which was dependent on its contracts for oil with the Ukrainian government, demanded that the Poles send the Czechoslovaks the oil that had been paid for to the Ukrainian government. The Poles refused, stating that the oil was paid for with ammunition that had been used against Polish soldiers. Although the Czechoslovaks did not retaliate, according to Polish reports the Czechoslovaks considered seizing the oil fields from the Poles and returning them to the Ukrainians who would honor their contracts.
On November 21, 1919, the Highest Council of the Paris Peace Conference granted Eastern Galicia to Poland for a period of 25 years, after which a plebiscite was to be held there, and obliged the Polish government to give territorial autonomy to the region. This decision was suspended on 22 December, 1919 and never implemented. On April 21, 1920, Józef Piłsudski and Symon Petliura signed an alliance, in which Poland promised the Ukrainian People's Republic the military help in the Kiev Offensive against the Red Army in exchange for the acceptance of Polish–Ukrainian border on the river Zbruch.
Following this agreement, the government of the West Ukrainian People's Republic went into exile in Vienna, where it enjoyed the support of various West Ukrainian political emigrees as well as soldiers of the Galician army interned in Bohemia. Although not officially recognized by any state as the government of West Ukraine, it engaged in diplomatic activity with the French and British governments in the hopes of obtaining a favourable settlement at Versailles. As a result of its efforts, the council of the League of Nations declared on February 23, 1921 that Galicia lay outside the territory of Poland and that Poland did not have the mandate to establish administrative control in that country, and that Poland was merely the occupying military power of eastern Galicia, whose fate would be determined by the Council of Ambassadors at the League of Nations. However, the Conference of Ambassadors in Paris stated on July 8, 1921 that so called "West Ukrainian Government" of Yevhen Petrushevych did not constitute a government either de facto or de jure and did not have the right to represent any of the territories formerly belonging to the Austrian empire. After a long series of negotiations, on March 14, 1923 it was decided that eastern Galicia would be incorporated into Poland "taking into consideration that Poland has recognized that in regard to the eastern part of Galicia ethnographic conditions fully deserve its autonomous status." The government of the West Ukrainian People's Republic then disbanded, while Poland reneged on its promise of autonomy for Eastern Galicia.
Approximately 10,000 Poles and 15,000 Ukrainians, mostly soldiers, died during this war. On July 17 a ceasefire was signed. Ukrainian POWs were kept in ex-Austrian POW camps in Dąbie (Kraków), Łańcut, Pikulice, Strzałków, and Wadowice.
Following the war, the French, who had supported Poland diplomatically and militarily, obtained control over the eastern Galician oil fields under conditions that were very unfavorable to Poland.
In the beginning of the Second World War, the area was annexed by the Soviet Union and attached to Ukraine, which at that time was a republic of the Soviet Union. According to the Yalta Conference decisions, while the Polish population of Eastern Galicia was resettled to Poland, the borders of which were shifted westwards, the region itself remained within the Soviet Ukraine after the war and currently forms the westernmost part of now independent Ukraine.
Although the 70 to 75 thousand men who fought in the Ukrainian Galician Army lost their war, and their territory was annexed by Poland, the experience of proclaiming a Ukrainian state and fighting for it significantly intensified and deepened the patriotic Ukrainian orientation within Galicia. Since the interwar era, Galicia has been the center of Ukrainian nationalism.
According to a noted interwar Polish publicist, the Polish–Ukrainian war was the principal cause for the failure to establish a Ukrainian state in Kiev in late 1918 and early 1919. During that critical time the Galician forces, large, well-disciplined and immune to Communist subversion, could have tilted the balance of power in favor of a Ukrainian state. Instead, it focused all of its resources on defending its Galician homeland. By the time the western Ukrainian forces did transfer East in the summer of 1919 after having been overwhelmed by the Poles, the Russian forces had grown significantly and the impact of the Galicians was not decisive.
After the war the Ukrainian soldiers who fought in this war became the subject of folk songs and their graves a site of annual pilgrimages in western Ukraine which persisted into Soviet times despite persecution by the Soviet authorities of those honoring the Ukrainian troops.