Why did Tsarism collapse in February 1917?

There are two main reasons why Tsar Nicholas II abdicated in February 1917, leaving behind a Provisional Government. The first reason is the First World War. The second, interrelated reason is Russia's weak economy. The First World War intensified Russia's pre-existing institutional and economic difficulties. The Army used outdated tactics which led to dreadful losses - for instance, at the Battle of Tannenberg. (There were, however, some successes - for example, General Brusilov inflicted 1/2 million Austrian casualties). When Nicholas declared himself Supreme Commander of the Russian Army, he was personally blamed for these defeats, breeding discontent.Arguably, the most important reason is the economy. Orlando Figes said that the "revolution began in the bread queues." After two years of war, the railway system simply collapsed and were incapable of handling freight by 1916. For example, in Archangel (a northern port), the pile-up of undistributed goods was so great the tracks began to sink into the ground. By 1916, Moscow and Petrograd, Moscow and St Petersburg received only a third of their food and fuel requirements. As a result, in February, Petrograd was paralysed by strikes. Most of the 150,000 troops at the Petrograd Garrison had deserted, and the army and police were unable to restore order.