Which country's civil war of 1936-39 preceded WWII?

Spain, and it was the rehearsal in a fairly literal sense. Germany and Italy supplied Franco with aircraft, tanks and men; the Soviet Union supplied the Republic; and Britain and France ran a non-intervention policy that in practice starved only one side. The German Condor Legion used it to test tactics that reappeared in 1939 - Guernica was among the first demonstrations of what bombing a town would do.

It also drew in around 35,000 foreign volunteers in the International Brigades, which is unusual - people from fifty countries travelling to fight in someone else's war for a political idea. Orwell went and was shot through the throat; his account describes not only the fascists but the Soviet-directed suppression of rival left-wing factions, which is where his lifelong anti-Stalinism comes from and which fed directly into 1984.

Spain then did not speak about it for decades. Franco ruled until 1975, and the transition to democracy was built on a pacto del olvido - a pact of forgetting - with an amnesty and no reckoning. That held until the 2000s, when descendants began exhuming mass graves; Spain still has more people missing in unmarked graves than any country except Cambodia, and the politics of digging them up remains bitter.