Let's assume that one of the droughts which periodically afflicts Russian agriculture begins in 1915, causing major crop failures and famine (we'll assume that this is localized to Russia and Ukraine, and doesn't affect the rest of Europe too much). By the spring of 1916, peasant revolts in the afflicted areas have required significant numbers of Russian troops to be re-deployed out of the front lines to put them down. This allows the Germans and Austrians to resume their successful offensives of the previous year, pushing the Russians completely out of Poland and into Russia itself. Romania, seeing Russia teetering on the brink of collapse, joins the Central Powers and invades Russia as well in July 1916.
The drought continues as the summer of 1916 drags on, and once again, the crops fail. There are more revolts, not only by the rural peasants but in the cities as well. The Tsar orders his soldiers to put them down, but now, the soldiers refuse to fire on the peasants and workers. A mob of workers and soldiers marches on the imperial palaces in St. Petersburg, and the Tsar barely escapes with his family. As per OTL, they are captured by soldiers outside the city and forced to abdicate in September 1916.
The Russian armies, with the political situation behind them collapsing, melt away, and the Germans, Austrians, and Romanians advance deep into the Ukraine, occupying most of it by the time the snows come in November 1916.
A Provisional Government under Alexander Kerensky doesn't even consider attempting to continue the war, and sues for peace on December 1, 1916. The Treaty of Kiev is signed on Christmas Day, 1916, with terms similar to the OTL Treaty of Brest-Litovsk.
Now, the Germans and Austrians can redeploy the bulk of their forces to the west in the spring of 1917, giving them the ability to launch major offensives there a year earlier than in OTL.
What are the effects of all this?
The drought continues as the summer of 1916 drags on, and once again, the crops fail. There are more revolts, not only by the rural peasants but in the cities as well. The Tsar orders his soldiers to put them down, but now, the soldiers refuse to fire on the peasants and workers. A mob of workers and soldiers marches on the imperial palaces in St. Petersburg, and the Tsar barely escapes with his family. As per OTL, they are captured by soldiers outside the city and forced to abdicate in September 1916.
The Russian armies, with the political situation behind them collapsing, melt away, and the Germans, Austrians, and Romanians advance deep into the Ukraine, occupying most of it by the time the snows come in November 1916.
A Provisional Government under Alexander Kerensky doesn't even consider attempting to continue the war, and sues for peace on December 1, 1916. The Treaty of Kiev is signed on Christmas Day, 1916, with terms similar to the OTL Treaty of Brest-Litovsk.
Now, the Germans and Austrians can redeploy the bulk of their forces to the west in the spring of 1917, giving them the ability to launch major offensives there a year earlier than in OTL.
What are the effects of all this?