I'm not as keen on having my nation behave offensively on the world stage. We have been noted as a defensive nation traditionally, but as I'm sure that you know or suspect, that all changed admist middle east issues, particularly 911.
Traditionally, America was more neutral when it came to global issues, at least during the 18th, 19th, and early 20th centuries. I don't know if I would characterize our policies as "defensive," but we were content to remain mostly a regional power in our own hemisphere, while refusing to take sides in the conflicts which embroiled the nations of Europe.
The big change in U.S. policy occurred during World War I, when Wilson declared that we needed to fight to "make the world safe for democracy." However, at the time, the U.S. was not yet ready to enter the League of Nations or take the lead on the world stage. That wouldn't happen until World War II, which the Japanese so graciously invited us to enter, earning the praise of U.S. imperialists and warmongers. At that point, there would be no turning back. This was especially true after the war, when the French and British Empires were in receivership, and the U.S. had to fill the global power vacuum that other powers (mainly the USSR) were wanting to take over.
That's what put us in places like Korea, Vietnam, Iran, as well as elsewhere in the Middle East, Asia, and Africa. 9/11 was merely the backlash against us for the policies we embraced for the sake of other nations, not our own.