It is prudent to approach the U.N., NATO, and E.U. as the foreign policy actors. The main reason for engaging these three actors is that they handle various issues (Smith, Hadfield & Dunne, 2016). Additionally, they have numerous member states, and this means that most of the policies that the organizations initiate will be favorable. In addition, the USA has been an ally to many nations that are members of these unions, which implies that they have a common interest.
The most advantageous school of thought for the United States to follow in the future is the formation of allies. When the nations form partners with other states, the associates will allow goods and services to pass through their borders without restrictions. It will also enable easy movement of people from one nation to another, thus eliminating illegal terrorizing activities due to tension between countries.
Reference
Smith, S., Hadfield, A., & Dunne, T. (Eds.). (2016). Foreign policy: Theories, actors, cases. Oxford University Press.