It's not a proven fact, just Cold War propaganda. Socialists didn't start two world wars, capitalists did that. Moreover, all socialists aren't Marxists, because Hitler wasn't a Marxist and yet he was a socialist. There are different types of socialism. Nonetheless, the USSR didn't murder millions, it fought to defend itself, against the invasion of its country in 1918, by the US, Britain, France and 11 other countries. It also had to fight 4 million German invaders. So the people that the USSR killed, were either foreign aggressors or traitors like you, who were fighting on the side of capitalists and kings (Tsars). and deserved exactly what they got.