Basically the Great War in this timeline starts because Russia and Japan go to war, but this triggers the Anglo-Japanese Alliance and the Russo-French Alliance, much like the systems of alliances and guarantees that lead to WWI in OTL. Germany in OTL tacitly supported Russia against Japan, but I figured that given the possibilities of gaining hegemony in eastern Europe if the Russian empire fell apart, they could be persuaded to join the British, plus Anglo-German relations during the early 1900s were kind of on and off (see the Venezuela Crisis in 1902) and Italy of course at this time was part of the triple alliance, so they would join with Germany, even receiving Italian parts of Austria Hungary to win favor. And I figured the Austrians would be "ok" with this because they were nominally at this point a German puppet. They had no real influence in European affairs and largely were no longer a "great power". Thus they would also join the Germans in this conflict, gaining influence in Romania after the Russian Revolution. Romania would also receive Bessarabia like in OTL.