The First World War and the February Revolution.
The First World War had two main effects on Russia: firstly a huge number of men lost their lives, and secondly it caused economic chaos. On 8 March 1917 women in St Petersburg went on a strike for 'bread and peace', starting the February Revolution.
As part of your revision, think about the arguments and facts you would use to explain:
What caused the uprising?
Why did the monarchy collapse?
In 1917, the Russian monarchy collapsed. There are three main theories as to why:
“The immediate cause of the February Revolution of 1917 was the collapse of the Tsarist regime under the gigantic strain of World War I. The underlying cause was the backward economic condition of the country, which made it unable to sustain the war effort against powerful, industrialized Germany.”
Philip E Mosley, late Professor of International Relations, Columbia University
Notice how he doesn't choose one of the three factors as being the cause of the Revolution. Instead, he suggests that the revolution was caused by a mixture of all three factors working together - the underlying weaknesses of the government meant that, when he was faced by problems during the First World War, the tsar could not cope with them and fell from power.
You may wish to take this as your overview conclusion of the causes of the February Revolution of 1917 in Russia.