Tit for tat, huh? As the only arsenal of freedom in the world, the US must maintain adequate manufacturing capabilities to meet the needs of an immediate war. The US can't rely on another country for this. US industrial capacity has bled out to other countries over the years, many of them hostile to us. It really is a matter of national security.
Most European countries are reliable allies for the US only when asking us to intervene on their behalf. Canada has taken advantage of far too favorable trade terms with the us. Finally, the political rhetoric and internal actions of these countries are getting to be somewhat anti-thetical to ours. I think, for example, that many European countries will side with arab countries over the US if push comes to shove. Individual freedom is under stark attack in those countries as well.