Question

What marked the end of the Russian monarchy

Answer 1

the execution of the tsar and his family

Answer 2

The main event that ended the Russian monarchy was the February Revolution. It was a spontaneous demonstration against the Tsar's government which turned riotous and spread to many other cities. The Tsar tried to order police and military forces to put down the riots, but they refused to obey him. In fact, many soldiers even joined in the riots. 

Tsar Nicholas realized that the only way to end the violence was to abdicate his throne. He signed the abdication papers in March 1917 ending 300 years of the Romanov monarchy. The Provisional Government was instituted to govern the country until a Constituent Assembly could be seated, but the Provisional Government was overthrown in the October Revolution also known as the Bolshevik Revolution. The Bolshevik Revolution is not the revolution which ended the Russian monarchy, because the monarchy had already ended 8 months earlier.

In addition, the Tsar and his family were not killed during the Russian Revolution. They were kiled by the Bolsheviks during the Russian Civil War in July 1918, nine months after the October Revolution had ended.