I think that it's an historical accident that the United States has ended up fighting wars around the world. In the years before both World War I and World War II, most people in the US were perfectly happy to stay at home and let other people fight in foreign lands. But at the end of WWII, it became clear that the US and the Soviet Union were the two great powers. Due to its anti-communist/pro-capitalist sentiments, the US overcome its isolationist leanings and started to oppose the Soviet Union all over the world. Thus, the US became used to fighting in foreign wars (Korea, Vietnam) and playing a role in other conflicts.
In the post-Cold War Era, neo-conservatives have shifted the US's focus from the communists to "Islamofascists." But even now, many people in the US would rather focus on issues at home.