The negative unintended consequences of war are so great that most wars have a negative outcome. Americans have a high opinion of their military adventures but really only remember a few of them. Every war the United States fights and forgets becomes the most significant historical event in the country where we waged the war. There are foreigners who hate us for wars, Americans don’t even remember fighting.
Did the United States need to fight World War 2? Yes, we did, but only because we had been an imperialist nation in the Pacific in prior decades.
So, why does the United States fight wars? Some say it is to spread democracy around the globe. It would make more sense to give representative government to others, if only we had it ourselves. The US government operates independently of the will of the constituents. Americans support wars because it is another dishonest way of increasing self esteem. Spreading democracy around the globe makes Americans feel good about themselves. Never mind the fact that we are not actually spreading democracy. The goal is to feel good and that gets accomplished, just dishonestly.