A. Bill Clinton was the <span>first U.S. president to visit Vietnam since the end of the war.</span>
The earliest involvement would be because of the cold war.
In the past, the soviet union was having an interest to make Afganistan one of their ally (due to high value of natural resource that Afghanistan has)
To handle this situation, united states Give a supply of weapons, soldiers and financing to the group that stand in opposition of Soviet Union's influence. But after the opposition manage to get rid of soviet influence, a new group called taliban started to control that region and ending up in a mess that we see today.
Don't know the exact answer for the first one, but the second one is Thomas Hobbes.
A body of fundamental principles or established precedents according to which a state or other organization is acknowledged to be governed.
Presidential Succession Act. The Constitution also didn't indicate who would assume the vice-presidency I think
