World War Which
Ilan Goldenberg goes beyond the observation that for conservatives it's always 1938 and notes the opposite lessons of World War I where various sides deemed themselves "forced" to fight a war nobody wanted and that served nobody's interests.
My strong sense is that 1914 scenarios are more common than 1938 scenarios. Trade and tourism are positive-sum interactions between nations. War and coercive acts short of war are negative-sum interactions. This means you should try very hard to seek peaceful intercourse via trade and tourism and to avoid negative-sum conflict-based interactions. Sometimes, of course, one faces a foe so determinedly fanatical that it's impossible to avoid the negative sum track where everyone invests vast resources in figuring out better ways to blow stuff up. But the kind of strong irrationality represented by a Hitler or perhaps a Pol Pot is very rare, normally people can't acquire and maintain political power without being sensitive to their own interests.