This week is the hundredth anniversary of the second Russian Revolution, one of the most transformative political events in the history of the modern world. Here are five facts you should know about the world’s most destructive revolution:

1. The second Russian Revolution (the Bolshevik Revolution) began on November 6 and 7, 1917. (Because the Russians were still using the Julian calendar, the date for them was October 24 and 25, which is why the event is often referred to as the October Revolution.) It was the second of two revolutions in Russia in 1917. The first, which occurred in February, overthrew the 300-year rule of the imperial Romanov dynasty, while the second placed the Bolsheviks and their leader, Vladimir Lenin in power.

2. After the fall of the czarist government in February, the Russian parliament appointed the Provisional posed of leaders from the middle class capitalist class. In response, Lenin called for a government that would be ruled directly by “soviets.” The Soviet was a local council of delegates that represented soldiers, peasants, and workers and which performed both legislative and executive functions. In March the Petrograd Soviet of Workers’ and Soldiers’ Deputies, the soviet in the city formerly known as St. Petersburg, had gained so much power that it was able to issue its famous Order No. 1, which directed the military to obey only the orders of the Soviet and ignore those of the Provisional Government.

3. The Bolsheviks (a name which means “one of the majority”) were originally a faction of the Marxist Russian Social Democratic Labor Party. Founded by Vladimir Lenin and Alexander Bogdanov in 1903, this group—also known as “Reds”—had gained majorities in the powerful Petrograd and Moscow Soviets by 1917. They refused to share power with other parties and over the next few years became the dominant force in Russian politics. They changed their name to the Russian Communist Party (of Bolsheviks) in March 1918; to the All-Union Communist Party (of Bolsheviks) in December 1925; and to the Communist Party of the Soviet Union in October 1952.

4. In the first week of November the Bolsheviks and the Left Socialist pletely took over the government in a nearly bloodless coup. By occupying strategic locations, such as government buildings and telegraph stations, they were able to overthrow the Provisional Government within a few days. The Second All-Russian Congress of Soviets, which convened in Petrograd simultaneously with the coup, approved the formation of a new posed mainly of missars with Lenin as it’s leader. Lenin thus became the dictator of the world’s munist state.

5. The Russian Revolution sparked the world’s costliest civil war. The Russian Civil War lasted five years and is estimated to have claimed 1.5 batants and around 8 million civilians. Most of the civilians died because of armed attacks, disease, and famine. The warring factions included the Red Army, which fought for Lenin and the Bolsheviks, and the White Army, which consisted of diverse factions of monarchists, capitalists, and socialists. The conflict ended in 1923 with Lenin’s Red Army claiming victory and establishing the Soviet Union.