I think its a becuse i look back and saw thats what it was
Not exactly. There was an exact line. Anything below that line would be slave states. Anything above would not.
type in the exact questions you have into google. Then search on the websites. They provide the exact answers.
Ps. It is a lot.
Two of the main reasons for Truman's policy of containment during the Cold War were that the USSR was trying to rapidly expand, and that eliminating communism where it already existed was extremely unlikely. It was considered a very effective policy originally but then was viewed with skepticism when Vietnam hit.
Fog, the other three options would be too high in the atmosphere to cause visibility problems.
