I've always wondered what America would do if it decided to hold a war, sent the UK an invitation RSVP but received a reply to the effect that owing to a prior commitment we are unable to attend.
Why would you want to do that? We've been allies for most of the last 400 years. To quote a piece in Wikipedia:
"The United States is bound to Britain by shared history, a common language and legal system, culture, and kindred, ancestral lines in English Americans, Scottish Americans, and Welsh Americans, which can be traced back hundreds of years."
http://en.wikipedia.org/wiki/United_Kingdom%E2%80%93United_States_relations
A lot of the above is true of many other countries around the world.
IMO, what really needs to happen is the elimination of massive wars in favor of limited tactical special ops actions.