Why doesnt every country just stick to themself??

i know for now we "need" eachothers crap, but why cant be all develope our own means of everything, so we never need to rely on anybody. Why we kill all these people to defend another country is beyond me. If you live in america you should stay and defend here. If you live in china you should stay and defend there. Why is it that all our countries have to get involved with one another SURE it would be just wonderful if we could all get along but its never going to happen. it never has, and 99% chance it never will. If the president cared so much about iraq and wanted to change peoples lives in other countries, while our people go to ****, then why didnt he run for office in some other country. if people in ethiopia are starving, stop breeding and raising kids into a starving world, it would then eventually cease to exist with no breeding. It just pisses me off that we still dont have running water everywhere in america but oh we need to go and worry about iraqis