India would be a fantastic major ally for the US - a developing democracy, with religious and ethnic pluralism.
Hopefully a Federal EU in the future,
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China could be a good ally, though I doubt China will ever work truly consider the US an "ally."
UK and France are good allies due to their blue-water navies. Brazil could potentially be as well, if it cleaned up its government from rampant corruption.
Israel is a good ally, though the US needs to be more aggressive in making sure Israel's government toes the line and is more aggressive in pursuing a two state solution and punishing settlers.
I think both Azerbaijan and Georgia would be decent allies, although the former is a kleptocratic dictatorship and the latter is very weak militarily. Both need a major ally since Armenia and Russia work together and are aggressive toward the two.
Indonesia has the potential to be a really good "backdoor ally." Most of Indonesia diplomatic power comes from being independent of the major powers, which makes it the most powerful negotiator between the Muslim-majority countries. Thus, I think the USA needs to be in Indonesia's good graces.
Japan and SK are necessary allies for power projection in East Asia and the Pacific. The US needs to be more explicit in its disapproval of Japan's attempted rearmament.
