Why did many Americans fear Vladimir Lenin and his followers, the communist?

Vladimir Lenin had successfully brought the USSR on the global stage after the Communist Revolution. At the time the Russian Empire was growing unstable but it still was the biggest country in the World. This could strike fear in the eyes of Americans as the biggest country had collapsed and turned into a Communist powerhouse. This would've most likely caused a 'Red Scare" in the US and Europe. As Russia was the advocator of Communism, places in the US also had small communist uprisings which made citizens even more unsettled.