A point of accuracy here:
Since Vietnam and the occasion on which 17 GIs got killed and 51 were injured in a shoot out in a Somalian market the US has not been 'most willing to go into other countries and lend a hand against terrorism attacks world-wide.'
The US has however been more than willing to launch cruise missiles against terrorist targets and quite rightly so many people would say. There is a important difference between those two policies. One endangers the lives of servicemen the other does not.
The US has been willing to act in a peacekeeping capacity and invade other countries to maintain the peace (and oil supplies) but there is a difference between that and anti-terrorist operations. In anti terrorist operations your soldiers are a target every day and you will lose soldiers regularly-examples are Northern Ireland, Israeli occupation of the West Bank, Spain etc etc
The US government has repeatedly shown that the protection of its servicemen is of prime importance-even below the importance of retailiation in some cases.