Switzerland is a very special case - at that time, they were holding most of the public and private funds (of political leaders) in Europe. No one would dare disrupt their own economy during war. Funnily enough, cryptocurrencies might be the end of Switzerland's neutrality and financial importance :)

The US has very few natural resources and taking over this country's land is relatively pointless. However, as the World's Police, as they are often referred to, they often meddle in other country's politics (and to get to their resources too, of course). This makes them a perfect target for hit and run tactics (terrorist attacks), which should, in theory, force the US population to vote against foreign intervention.

The reason why this hasn't happened yet, is because the US economy thrives on cheap fuels from other countries. As long as there's a conflict in the Arab world, fuel will be sold on the cheap, because local regimes and ISIS need cash for weapons - the more fuel they sell, the more weapons they will get.

The other major fuel producer, Russia, is not at all happy that Arab fuels are cheap - they have to lower their own prices as well, which makes their shaken economy even weaker. This is why they recently intervened in the conflict and support the pro-Russian government of Assad.

Now consider all of the above - the US has to fear Arab terrorists (who don't like the idea of a meddling World Police), Russians (who don't like America's plan for cheap fuels), as well as local political radicals, which act as terrorists as well. That's the price of having cheap fuel - living in fear.

Soon they will have another problem - their main export destination, Europe, will have a huge cheap workforce of Syrians, which means that the US may end up importing more than exporting - in effect making their economy weaker.