The Bolsheviks betrayed Russia at the behest of the Kaiser during wartime with the express goal of destabilizing Russia from within. They didn't overthrow the Tsar (a huge chunk of bolsheviks were paid police informants anyway) but instead overthrew the democratically elected constituent assembly. Kerensky's provisional government was already on the outs, nobody except the hardest of the hardcore in the white army even cared about the Tsar anymore, there was no risk of a return to monarchy and the Russian people overwhelmingly supported the SR's, a socialist party that rivaled the Bolsheviks. Lenin flipped the table over and started a civil war that cost millions of lives out of ego - his egotistical belief that only the Bolsheviks could institute socialist reforms in Russia and that all other Socialist parties were betrayers of the revolution. To that end, the Bolsheviks spent almost as much time killing fellow socialists as they did actually fighting "monarchist" whites (mostly constitutional democrats and moderate socialists who allied with former army officers). Ask the Kronstadt sailors what life was like under the rule of Lenin, or the SR's, or most of the old guard bolsheviks that were chewed up and spat out by their own revolution. Ask the Poles, Latvians, Estonians, Finns, Ukrainians, etc. that were promised self-determination with the declaration of the rights of the peoples of russia (https://www.marxists.org/history/ussr/government/1917/11/02.htm) but were invaded because Lenin had no intention of following through on his promises. Ask the peasants that were bayoneted to death by red guard detachments because they wouldn't hand over their last sack of grain they needed to feed themselves. Ask the Petrograd workers who were forced back under the old bosses because Lenin needed war communism to fight his useless civil war he started. Ask why so many in areas of Europe and central Asia that were formerly part of the USSR/Russian Empire wanted out ASAP.