Oas , eu , and nafta are examples of

OAS, EU and NAFTA are all examples of what is known as a "trading bloc". These trading blocs promote free trade amongst neighbouring countries; OAS was a trade agreement amongst countries in the Americas (Both north and south), NAFTA was only amongst North America (US, Canada and Mexico) while the EU goes slightly further; incorporating free trade with free movement of people, amongst 28 European countries. Although NAFTA is largely considered to have failed, OAS has had some success, while the EU is largely successful (I live in Ireland and I can get something from Greece for the same price as it costs in Greece for example.)

Hope I helped and please rate my answer :)