You can never be sure anyone ever actually prevented a war. However, an argument could be made that Reagan might have prevented further cold war conflicts by his buildup of American military power and his clear indication of his willingness to utilize it if necessary. That’s how wars are prevented - through strength and the willingness to use it when necessary.
Now you are moving the narrative towards an inconvenient truth.
Hit yourself on the nose with a newspaper.
The so-called "anti-war" left are full of it. They aren't really anti-war. They're just anti-American military victories. They've never met a bloody leftist uprising they didn't support. They worship mass murderers like Mao tse Tung. They are anything but pacifists.