One of the key factors that lead to the successful Bolshevik revolution was the mutiny of Commander Kornilov with his small army with plans to take them to Petrograd, remove the Preliminary Government from power, and set up a military dictatorship. Kerensky - the effective "Prime Minister" - had no army of his own within Petrograd or any nearby areas as they were all fighting at the front. As a result the Provisional Government had no choice but to give weapons to the Bolsheviks to protect the Provisional Government. This worked hugely in favour of the Bolsheviks as now they had weapons, only the Tsar would have been stupid enough to order them to give the weapons back. This is a direct result of the stress of the war on the people of Russia, even the Commanders of the army. If the Provisional Government had pulled out of the war and made piece with the Kaiser then Kornilov wouldn't ever have caused a mutiny, leading to the arming of the Bolsheviks.
Another key factor that lead to the revolution would be the Provisional Government's failure to deal with the land problem. This is a key factor in my opinion because this was one of the mistakes that the Tsar made. This was a vicious cycle, the peasants wanted more land so they decided to steal the land from other land owners and upper-class men. Because of this more people started to dessert the army, either to protect their own land, or to make sure they got some of the land before it