I'm working an a Master's Degree in History. Are you saying that America isn't good at war?
I'm happy for you that you're pursuing further education. I went through that route too, in a different subject though. I know getting a masters degree is very hard and requires a lot of effort.
As far as America's capabilities at war: I didn't say America isn't good at war. In fact it possesses the best technology and one of the biggest men power, which gives it an edge. When you combine these with great tactics and strategy, you see a highly capable war machine, which wasn't very successful in Vietnam nor Iraq. Both terrains created big challenges for the US army and there were a lot of casualties, which bugs me a lot actually.