Albeit this is a basic answer, World War Two was a major catalyst to an increased focus on internationalism. In addition, financial and political interests (most notably for political interests is the Cold War) are both legitimate reasons to why the United States of America has remained as a major part of international affairs.
Because that was the only support they could really get, mainly because the government always sided with the factory owners because they were the ones making the money for them. <span />
Interesting document.
It was issued by the German Foreign office (January 1917) proposing that Mexico should align itself with Germany in the even America enter the war. Germany was pleading for an alliance that would keep America busy dealing with an attack from the south. Fortunately it didn't work.
I believe it's "<span>the source of the Mississippi River."
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