You take comments too seriously.
While Vietnam was a mistake, it was because the US was fighting a Cold War against the soviets.
The first Iraq war was completely justified. Second clearly a mistake.
Historians believe that millions of lives and hundreds of thousands of American lives were saved by the atomic bombs. The Japanese weren't going to surrender without a fight until they could see the real risk that their homeland was going to be completely destroyed.
And you are ignoring the air strikes on Yugoslavia and the Korean War.
When you are the world leader (and not just part of the entourage), you will have to make bold decisions and sometimes they will be wrong. Unfortunately our current administration doesn't take the "world leader" thing seriously.
The US has a history of escalating military conflicts. It is again occurring today. I believe there is a false sense of security of many Americans because they feel removed from the battle. The American reaction to 9/11 suggests this. During the Cold War, the US and USSR could have destroyed each other entirely ( if not much worse ). At some point, Americans have to understand that the only true protection is diplomacy, good intentions, and seeking peace. Military can be used to protect your borders and as a last resort to prevent immoral acts to humanity like genocide. If a country like USSR or the US itself somehow goes rogue and decides to annex other nations, then many nations can band together and suppress the aggressor if needed. Again, a last resort.
After WW2, many nations said "never again". Some Americans never got the message.