How did two revolutions in 1917 end the tsars?

Strikes, hunger and a mutinous army ended the monarchy in the first revolution, in February 1917 by the calendar Russia used then, and the Bolsheviks seized power from its successor in the second, in October. In modern dates they fell in March and November. Together they ended the rule of the tsars and began the Soviet state.

Start with the war. German victories on the Eastern Front and logistical problems causing shortages of bread and grain left the Russian army losing morale, with large-scale mutiny looming. The Tsar made it worse by taking personal control of the army in 1915, a challenge far beyond his skills, and he was held personally responsible for the defeats.

Then came the winter's strikes. International Women's Day rallies turned into economic and political gatherings, with demonstrations demanding bread supported by the industrial workforce. The Tsar ordered the army to put down the rioting, but around 12,000 reliable troops were reluctant to move on a crowd with so many women, and troops began to revolt. Nicholas II stepped down on 15 March, ushering in a provisional government led by the Duma. Russia now had two rival governments: the Provisional Government and the network of Soviets.

The Bolsheviks won popularity with a program promising peace, land and bread, while the Provisional Government kept fighting the war despite public opposition. On 7 November 1917 the Bolshevik party organised an armed seizure of power in Petrograd. Lenin was in hiding, and the initial assault occurred largely without any human casualties.

Afterwards, in elections on 25 November, the Bolsheviks received 25% of the votes and the Socialist-Revolutionaries 58%. The Bolsheviks dissolved the Constituent Assembly in January 1918. Whether October was a minority coup or a genuinely popular revolution is something historians have argued about: one school calls it a minority coup, another stresses its popular support.