I agree with Thucy's definition of war.
There's been serious talk of a NATO ground invasion of Libya. So I don't think that scenario is unlikely at all. They've been throwing this idea around for a while. There's absolutely no end game there, and their cowardly air strikes, coordinated with the anti-black rebels are not going to work. Either they launch an invasion, or they quit with their tail between their legs. A glorious defeat of NATO, in my view. Hope the alliance never recovers.
I think a war with Russia is possible. They were close in 2008. If the Georgians do something stupid again like annihilating Ossetian cities it's not out of the question. Russia's position is more secure now with sane governments in Poland and Ukraine now. Russia, unlike China, doesn't back down once provoked. And NATO, after licking its wounds from its failures, needs an excuse to continue its existence. Before it was Yugoslavia, now that all their puppet Yugoslav breakway states are NATO lackeys, they need a new enemy. Belarus isn't going to happen because Belarus doesn't bother anybody and unlike Libya, is well equipped at taking care of insurgents.
War with China is unlikely at this point, at least between the US and China. A more likely scenario is a regional war and possible US involvement. China has become more assertive in southeast Asia, for example. It could be a sign of more tension to come, especially if Japan ever becomes serious about getting out from under the US security blanket.
North Korea seems to always be a possibility. We're itching for the North to fire the first shot. All sorts of provocative acts have been done by the South, and then blamed on the North. But I don't think the North will bite. They continue to act very prudently in the face of aggression.
Iran is not going to happen. Iran to America is like that ally we treat like an enemy. They share America's interests more than they compete. They help us with Afghanistan. They're thrilled with the situation in Iraq. They helped us in Yugoslavia. They helped us with the Contras in the 1980s. They might shout about Israel and send money to Hamas, but we don't really care.
The Venezuela situation is a possibility. We have a large number of military bases in Colombia. We basically control the Colombian government. Farc leaders are sent to America and put on trial in kangaroo courts. We helped them "liberate" mercenaries from Farc control. If Colombia starts violating the sovereignty of its neighbors again, militarization is very possible. Depends on how reckless the Colombian government gets. Santos seems less belligerent towards Venezuela than Uribe, mainly I think because Colombia is dependent on Venezuela for trade.
My real list for the next war -
Libya - 70%
North Korea - 15%
Russia - 10%
Venezuela - 3%
All others, less than 1%