About eight million men surrendered and were held in POW camps during the war. All nations pledged to follow the Hague Conventions on fair treatment of prisoners of war, and the survival rate for POWs was generally much higher than that of combatants at the front. Individual surrenders were uncommon; large units usually surrendered en masse. At the siege of Maubeuge about 40,000 French soldiers surrendered, at the battle of Galicia Russians took about 100,000 to 120,000 Austrian captives, at the Brusilov Offensive about 325,000 to 417,000 Germans and Austrians surrendered to Russians, and at the Battle of Tannenberg 92,000 Russians surrendered. When the besieged garrison of Kaunas surrendered in 1915, some 20,000 Russians became prisoners, at the battle near Przasnysz  14,000 Germans surrendered to Russians, and at the First Battle of the Marne about 12,000 Germans surrendered to the Allies. 25-31% of Russian losses  were to prisoner status; for Austria-Hungary 32%, for Italy 26%, for France 12%, for Germany 9%; for Britain 7%. Prisoners from the Allied armies totalled about 1.4 million . From the Central Powers about 3.3 million men became prisoners; most of them surrendered to Russians. Germany held 2.5 million prisoners; Russia held 2.2-2.9 million; while Britain and France held about 720,000. Most were captured just before the Armistice. The United States held 48,000. The most dangerous moment was the act of surrender, when helpless soldiers were sometimes gunned down. Once prisoners reached a camp, conditions were, in general, satisfactory , thanks in part to the efforts of the International Red Cross and inspections by neutral nations. However, conditions were terrible in Russia: starvation was common for prisoners and civilians alike; about 15-20% of the prisoners in Russia died, and in Central Powers imprisonment 8% of Russians. In Germany, food was scarce, but only 5% died.

At which battle was the second largest group that surrendered?
battle of Galicia