It's all about religion and history.
The early spanish settlers of the "American" continent had to settle the whole continent. Through the adventure in combating Indians AND in making a wilderness into a civilised village, the American value came up. Then the settlers weren't spanish any more, but American. That's why Americans like to combat, it's already in the history.
And how did the spanish come on the idea to settle a whole continent? Because the early spanish settlers were very catholic. (We learned in school that Catholic religion demands a lot of self-will and solving problems by their own) To my mind that's why they succeeded in populating a whole continent.
And now many Americans still have that feeling to do everything by their own, and to fight the ones who challenges them.
Religion amd history, used as reasons for war, are the real causes of war. Religion should be modernised, and history should be seen as something which is over.