While this thread may give rise to a million viewpoints, I will try and be brief and stay on track of security.
The United States may be one of few nations that could possibly become isolationist. By that I mean fully self reliant requiring no import or export to survive.
Given the size of our oil reserves we very feasibly could become isolationist and with the advent of alternative fuels make the switch without skipping a beat.
http://www.eia.doe.gov/pub/oil_gas/p...e_Reserves.htm
True Isolationism however has not worked for any country for any length of time and would pose a definite problem for our chosen way of life.
Instead, we must promote our way of life for the world. While it may be argued that there is nearly no alturistic act, short of diving on a grenade to save fellows, we are in the business of promoting global peace and freedom. Many of our actions as a nation may have had arguably negative consequences, but our motives are in the right place...In order to maintain our freedom and way of life, others must enjoy similar freedom and prosperity.
Our own security here relies ever more so upon global stability. As RL pointed out, globalization has ensured that distance is no longer a defense. Until all nations have some form of freedom and relative prosperity we will continue to be both the subject of praise and scorn.