Worst war for USA?

[HerbS]

After being on vacation for nearly 2 weeks[On an Island in The 1000 Islands].I became friends with a Korean Conflict POW.We had great discussions[after a few beverages].Then he asked me,What I thought was the worst war the USA got into.The Civil War being among the top five.He of course put the Korean Conflict first.Then I told him that I would ask this forum to rank-order the top 5 wars the USA was in!The challenge is your's.Please rank your top 5!Then I will tell you who was the the most near choices!