Falklands War (1982)

[Clark Kent]

It was a very short war (10 weeks) between Argentina and the United Kingdom for the control of the Falklands Islands, in the South Atlantic.
But the most important fact is: it was the last war in the history where two western countries fought on opposite sides.

I doubt Thatcher considered Argentina Western..

Whether she considered it western or not is irrelevant. Argentina is in the Western hemisphere, speaks a European language, is overwhelmingly Christian, a highly developed nation, and, at the time, was firmly pro-US. Heck, if you want to bring "race" into it, Argentina is even pretty "white", and the vast majority of its population is of European descent. There is no way that it's not counted as Western.

But anyways, the war was a blatantly imperialist move by Argentina, ironically enough. The Falklands are British.

[Clark Kent]

Wikipedia gives a pretty good overview of what it means to be 'Western'

As an American, I don't really see the Orthodox-Catholic split as being too big of a deal when considering what is "Western", since I consider the far more culturally divergent South America, Australia, and Western Europe to all be Western. Plus, Israel, which isn't even Christian, is considered Western. I would add the rest of Europe (except Russia) and the Philippines to that map, and take away South Africa.