A) During the Cold War, the American governments foreign policy revolved around the concept of stopping the spread of communism on a global scale. However, after the Soviet Union fell and many of their satellite nations became independent, the US government had to adapt a different foreign policy. This new foreign policy would be extremely complex, as they had to deal with genocide (in countries like Bosnia and Herzegovina, and Rwanda), invasions (like Iraq invading Kuwait), and dealing with the acquisition of weapons of mass destruction by potentially dangerous groups (like Al Qaeda and Isis).
B) The US government has responded to this trend by continually being involved in foreign affairs. The US has helped in providing troops, financial aid, and organization to countries that were destroyed by warfare or harmful radical groups. As times change, America will continue this pattern of involvement in order to protect the rights of individuals all over the world.
Well... Think about it, you sent your son to die several thousand miles to die away from home. Who'd want to send your sons to go fight a war they never wanted to be a part of?
The Vietnam War intensified social, economic and political tensions as a result of a lack of public support for the war, a fall in the image of the presidency and distrust in the executive division in general, an acceleration in deficits because of military spending and an increase of poverty.