Saint Petersburg, which was actually known as Petrograd in 1917, was the imperial capital city of czarist Russia. The city had been founded by Tsar Peter the Great in 1703 and served as capital city and location of the primary governmental functions for most of the time between its founding and 1918. As such, it was the logical location for revolutionary demonstrations and actions as the reign of Nicholas II collapsed.
With the abdication of Nicholas II, the provisional government continued to use Petrograd as the primary location of government. Tensions caused by years of repression of workers and peasants remained unsatisfactorily addressed, however, and the situation was further aggravated by the disastrous outcomes from Russian military involvement in World War I. The Petrograd Soviet of Workers and Soldiers, formed in February, 1917, was able to gain support from groups that felt powerless under the circumstances. The Bolshevik Party, led by Vladimir Lenin, cooperated with the Soviet in forcing the end of the provisional government.