The nature of USA is to stay far away while others fight. That is why this artificial country was created a little more than 200 years ago far away from all civilization. This also helped greatly in WW2 as most of the world was destroyed while US was untouched.
I'd say the beginning of proxy war doctrine is after the mess in Vietnam that brought USA to the brink of demise, seeing that mess US regime realized that it is incapable of fighting any war and not fall part. So the decision was to fight wars through proxies as much as possible.
- The official strategy is under what's known as Nixon Doctrine which is basically US giving everything to any third party who would fight for United States, as long as they are the ones doing the fighting and dying not Americans. The most recent example is Ukraine where "US fights Russia to the last Ukrainian" as many of their officials have already publicly stated too!
- The unofficial strategy is through militant groups which in West Asia means radicals like Al-Qaeda and ISIS as the biggest names that are globally recognized to smaller groups like the Kurdish terrorists including PKK, CPI, and others like KPIK, PRMI, ...
USA never attack a country who show them eyes, see example of North Korea or Iran. If you want to face USA then talk to them in language which they understand. Being defensive against USA means you are giving him space to come over you. I don't know how much fire power Iran or north Korea has but they always talk on basis of equality not accepting USA supremacy.
USA attack a country when its 100% sure that its weak enough to defend itself like Iraq or Afghanistan.
Al Qaeda and ISIS are USA created organizations that are either serving USA interest in regions or helping in USA achieving its interest.