Answer:
Congress
Article 1 of the Congress is huge (just did a project), detailed explanation of the house and senate.
I think that the best answer is the geographic location: many other countries (Sweden for example) have tried being neutral at different times but did not manage to: but the fact that the US has only two boundaries, and that both other countries also have a history of fighting from independence from a European power, makes it possible that unless US decideds to get involved in international politics, it can be "left alone".
As of 2007, the richest 1% held about 38% of all privately held wealth in the United States. while the bottom 90% held 73.2% of all debt. According to The New York Times, the richest 1 percent in the United States now own more wealth than the bottom 90 percent.Today, the top 1 percent of households own more wealth than the bottom 90 percent combined.
