Agreed. We should be protecting our own borders, and that's about it. I think our reasons for invading other countries has more to do with economic interests (including lobbying) and/or protecting the status of the dollar than actual national security. Unfortunately, with so many foreign countries holding U.S. treasuries (which they could decide to dump at any time) and allowing the dollar to be the reserve currency of the world, we could suffer serious economic blows by isolating ourselves. I'd still rather take that chance though. There's a good chance that these things happen at some point anyway.
Much better to isolate ourselves by not intervening militarily than by starting trade wars with allies though. This is where Trump is making a mistake, and he appears to realize that based upon his going back and forth.