B. The U.S became involved with Vietnam to stop the flow of Communism. The U.S. believed in the Domino Theory, which is if one nation fell to Communism, the surrounding nations will fall too.
EMpires used trade for all sorts of reasons a few were to get and sell goods. Another was to exchange information and news. This also connected people far and wide from the main part of the empire. It was easier to rule empires when trade was established
