1. When entering the Vietnam War, the mindset was that of the Munich Conference in which the European powers appeased Hitler. The term "No more Munich's" was thrown around quite frequently and many assumed that Moscow was pulling all the strings in spreading communism, an idea called monolithic Communism. Paranoia combined with political pressure to not allow anymore countries to fall to communism ayed a large part in entering the war.
2. America's Cold War Paranoia blinded the country I to thinking that the solution was purely military when it was inherently a social, political, and economic problem. The Vietnamese on the other hand viewed Americans as just another conquerer trying to subjegate them. Was the war justified? In retrospect, no.
3. The Vietnam War unsettled the credibility of the goveremt widening the credibility gap and spreading distrust and dissent amongst the people. The idea of spreading freedom and democracy would be looked at under a closer lense.
4. America it seems did not learn the lessons of Vietnam when entering Iraq and Afghanistan. Nor did they care to. The military chose to forget the war and would not study it again until decades later. More evidence in neglecting lessons learned is evident by the Army's counterinsurgency manual not being written until 2006, 3 years after being involved in Iraq.