The First World War began in 1914, with the assassination of Archduke Franz Ferdinand of Austria. There was a confrontation between Austria and Serbia (he was killed by a Yugoslav nationalist). This initial confrontation triggered a series of alliances and led to to the Austro-Hungarian Empire and the Germans against the British, French and Russians. Thus it was essentially a battle of empires. Italy was party of the triple alliance with the Germans and the Austrians but chose initially not to enter the war as it understood this as a defensive alliance and saw Austria as the agitators. By 1915 they shifted allegiance and entered the war on the British side.
Meanwhile in Rome Fr Wenz was to die in 1914, famously followed a day later by Pius X, some say of a broken heart as he witnessed Europe disintegrate in spite of his impressive efforts for peace. Six months later the Jesuits elected their 26th Fr General. Wlodimir Ledochowski was from an Austrian/Polish aristocratic family and was to be general from 1915 to 1942. When Italy entered the war against Austria it was untenable for Ledochowski to stay in Rome, so he moved with the curia to Zizers, Switzerland, where he was able to govern with less disruption.
Jesuits were to serve as chaplains during the war on both sides. The Irish Jesuit Fr Willie Doyle was one who was outstanding, and awarded and commended for his bravery. He was to die during the Battle of Passchendeale after running here and there on the battlefield as an angel of mercy. The publication of his spiritual writings and diaries have generated great interest in Ireland, he has been declared a Servant of God and his cause for beatification is open. There is a blog on his writings here.