The First World War was indeed a major cause of the Tsar's overthrow in the February Revolution. However, it was not the sole factor – rather, it was a catalyst and a focus that allowed all the other preexisting factors to boil over into revolution.
The First World War caused a multitude of problems for the peasants of Russia, both at home and on the front. The vast majority of conscripts were from farming villages, meaning that less men were at home to till the soil and produce food – it also meant a general slump in food production as a whole, resulting in a shortage of grain to feed the hungry industrial workers in the cities. As the death toll of the backwards, ill-equipped Russian Army was devastatingly high, this meant that virtually everyone in Russia would lose someone they knew, regardless of social status. The lack of reliable supplies of food and basic commodities such as coal (most of it was going to the front) further crippled the economy, especially during the harsh Russian winter. This caused riots and protests to break out, ones that the once-Royalist troops were now unwilling to curb. Economic problems aside, the Tsar also made several extremely misguided decisions that further damaged his reign. While he intended to use the Great War to secure his status as Father of the People, Nicholas failed utterly in two respects. Firstly, he left directly to command the front – this meant that all the blame for every military defeat fell on his shoulders and not some scapegoat commander. He would no longer be able to divert the illwill of the people should defeats occur, and they did indeed. Secondly, he left the Tsarina in charge of running the Empire while he was away, and this was a disasterous choice on many levels. Tsarina Alexandra was a German-born princess, which naturally aroused severe animosity on the part of the people who were actually fighting the Germans. Even