The closest U.S. ally not in NATO

[Boris]

I feel that Japan has been drifting away from us rather than towards us though.  They're starting to become far more dependent on China (are we) and it's not really clear who will support whom if the US and China got involved or if China and Japan got involved in a conflict in 2030.

democracies don't fight one another, bro

[Boris]

democracies don't fight one another, bro

I saw something about this once... The Golden Arches Theory of International Relations, or something like that? That two nations which both have Mcdonalds Restaurants trading there have never declared war on each other?

then I guess we don't have to worry about a future Indo-Pakistani war given that both countries acquired McDonald's joints in the 1990s

[Boris]

invalidated by Russia-Georgia, 2008

[Boris]

btw, is Argentina really an "ally?" I can't imagine most Americans rooted for them in 1982.

And in terms of U.S. military commitments/support, the answer is either Israel or South Korea, but those are dependent on perceived external threats.

[Boris]

Also, England bombed Finland during WW2 and they were both democracies

This is probably the most straight forward exception to the theory. I wouldn't count Pakistan in the 1990s as a liberal democracy (nor did the civilian government really have all that much control over the military). But the UK wouldn't have declared war on Finland if Germany hadn't attacked the Soviet Union (and if the Soviet Union had not invaded Finland in 1939) and iirc did not directly engage Finnish units (they bombed Nazi positions in Finland before the formal declaration of war). It was basically an act to show solidarity with Soviet Union against Nazi Germany, not an actual attempt to engage and destroy Finnish military units.

If we go with Freedom Houses's designation of "free," "partially free," and "not free," I don't think there has ever been a scenario where two or more "free" countries have gone to war with one another, but that's only post-1973