Because a monopoly would end up making someone monopolizing the whole world to a point where no one can buy a business and would allow them to set their prices as high as they want.
Answer:
The trade expansion act.
Explanation:
I confirmed from a reliable source.
Unfortunately, you didn't share any following reasons so that someony could choose the correct one, but I am pretty sure that I can help you and name the main factor. Definitely, the point which caused a decrease in the size of the armed forces at the end of the cold war is that the US promised to decrease its armed forces as part of the peacetime agreement. I bet it will help you!