One reason that lead up to the deposition of the Tsar was the lack of food and fuel in Russia at the time. There was simply not enough to go around, people were becoming desperate and would do anything for food and resources. There was also terrible inequality in Russia, the peasants were treated like work animals. Continuously discontent, it is understandable that they would want to break the regime and take part in the revolt.
The February revolution was a revolution focused around Petrograd (now St. Petersburg). In the chaos, members of the imperial parliament, or Duma, assumed control of the country. Forming the Russian Provisional Government. The army leadership felt they did not have the means to suppress the revolution. Tsar Nicholas II, the last Tsar of Russia, abdicated.
A period of dual power ensued, during which the Provisional Government held state power while the national network of Soviets, led by socialists, had the allegiance of the lower-class citizens and the political left.
During this chaotic period there were frequent mutinies and many strikes. When the Provisional Government chose to continue fighting the war with Germany, the Bolsheviks and other socialist factions campaigned for the abandonment of the war effort. The Bolsheviks formed workers militias under their control into the Red Guards (later the Red Army) over which they exerted substantial control.
The First World War also had a major impact on the abdication of the Tsar. Russia was weakened after exerting its army and resources for such a prolonged period of time, the government could not afford a revolution, yet that was exactly what they got. It was effectively the worst possible time for Russia (from a governmental point of view), thus making it the best time for the revolutionaries. The bitterly cold weather was also a major factor, Russian troops were freezing and so unable to properly deal with protests. As were the protesters, their homes and children were freezing, encouraging them to revolt on their behalf not wanting to see them suffer.
Many factors together all contributed to the fall of the Tsar. They all built up until the breaking point, when the Tsar finally abdicated. From lack of food and fuel to cold weather, as well as the Tsars inability to rule effectively and as a strong leader that Russia so badly needed, they resulted in abdication.
