While I am a constructionist when it comes to the Constitution, you really can't compare the America of 1789 with the America and world of today. Back then, we were in what Alvin Tofler called a "First Wave Economy", meaning an essentially agrarian society composed mostly of sustenance farming and some manufacturing, particularly in the north east. Then we grew into a mostly industrial country, or "Second Wave Economy where we manufactured most of our own goods and were a major exporter of goods to other less industrialized nations. Today, in the "Third Wave Economy", we are very dependent upon the abilities of other nations to provide things essential to our modern way of life, and as such need to protect our interests in these other parts of the world. That is because we are shifting to a mostly information driven economy and have shifted much of our manufacturing base to developing countries where people will do the work for less money. Our economy is also VERY dependent on petro-chemical products like plastics, paints, etc. as well as fossil fuels. For that reason too we need to keep up a strong presence in otherwise useless (for our needs) parts of the globe.
This shift in economics is beneficial in times of peace, where we can take advantage of cheap labor to produce our modern-day "essentials" and improve the quality of life of the average and upper poor Americans. Unfortunately, it also makes us much more vulnerable. Should, say, China, decide it no longer wishes to trade with us, or OPEC or Venezuela take their oil away, our entire society would grind to a screeching halt. This was not the case even 50 years ago, but it is the case now. As I am laying in bed to write this right now, I am using a Chinese made Gateway Laptop. I have an Apple iPod next to me and it was made in China. My Motorola Razr cell phone that is also on my bed with me is made in China. In fact, probably 90% of the items in my room come from foreign manufacturing facilities. The Chinese have become quite good at making precision castings and electronics with decent quality. Take away the stability of any of the countries that we do a decent amount of business with and you hurt the average American. In fact, lack of stability is pretty much the only reason we do almost nothing with African countries and only limited trade in South America. We need to take a major role in world politics to protect our interests and those of our trading partners in order to preserve our own quality of life. This means alliances and making deals with some otherwise unsavory characters like Pervez Muscharif. It is too complex a world to just opt out of the affairs of other countries.