Suing for peace is an act by a warring nation to initiate a peace process. Suing for peace is usually initiated by the losing party in an attempt to stave off an unconditional surrender and may sometimes be favorable to the winning nation, as prosecuting a war to a complete or unconditional surrender may be costly. In this case, then, the word "sue" is being used in its original, now-obsolete meaning of "to make petition to or for", rather than the usual meaning of "to take legal action against".
Pressing for peace may sometimes, however, be started by the winning faction as a means to end the war for several reasons, such as where additional conflict would not be in the perceived best interest of the winning party. In this case, demands might be made, or the two nations may agree to a "white peace," or status quo ante bellum.
Suing for peace Wikipedia
The First Sino-Japanese War (1 August 1894 – 17 April 1895) was fought between the Qing Empire of China and the Empire of Japan, primarily over influence of Korea. After more than six months of unbroken successes by Japanese land and naval forces and the loss of the Chinese port of Weihaiwei, the Qing government sued for peace in February 1895.
The archives abound with attempts to halt World War I, but most attempts were unofficial and of no effect. On 2 December 1916, prior to his coronation later that month, Charles I of Austria took over the title of Supreme Commander of the army from Archduke Frederick. In 1917, he secretly entered into peace negotiations with France. He employed his brother-in-law, Prince Sixtus of Bourbon-Parma, an officer in the Belgian Army, as intermediary. The negotiations of the Sixtus Affair for a sued peace failed.