What event do you think started the Cold War

In my opinion In June 1950, the first military action of the Cold War began when the Soviet-backed North Korean People's Army invaded its pro-Western neighbor to the south. Many American officials feared this was the first step in a communist campaign to take over the world and deemed that nonintervention was not an option.

Or you can put

The fight against subversion at home mirrored a growing concern with the Soviet threat abroad. In June 1950, the first military action of the Cold War began when the Soviet-backed North Korean People’s Army invaded its pro-Western neighbor to the south. Many American officials feared this was the first step in a communist campaign to take over the world and deemed that nonintervention was not an option. Truman sent the American military into Korea, but the Korean War dragged to a stalemate and ended in 1953.

They weaken the south vietnamese army.