Yes, this blog is going the artisanal slow history route!
1939: The year that the state spent more on technology than any other (peace) year ever. Is that how you know 1939? No, you know 1939 as the year war came. The two are of course related, but in a way that is none too obvious. In the received version that I learned from Professor Strawman’s 1962 bestseller, I Tossed Off This Book During A Sabbatical I mostly Spent Drinking Myself Stupid Around London, I learned that the Western Democracies entered the year humiliated by their surrender of (nice) Czechoslovakia to the Dictators at Munich, and exited it in a self-chosen world war for Poland. Because Britain didn't spend enough on defence. (I think France might have been involved in this, too, but I don't find "France" in the Professor's index). Also because Neville Chamberlain was dumb, dictators were bad, and, uhm, Cliveden Set something something.
A few years later, I learned from Duncan Cameron Watts that it looked like the German economy was collapsing in the spring of 1939, even as Hitler went on a rampage of aggression and menaces that led to the Allies finally standing up against him: in January, not March, being the substantive point of a well-written and not that old book that for some reason shows up on the third page of results in a Google Books search for "d c watt How War Came" after two pages of citations. Google Book's search algorithms could do with some tweaking.
Even more recently, I learned that the Allies were optimistic going into the war. That they thought that they would win (which, after all, they did) because they were stronger. And even more recently, Adam Tooze has shown that they were, in fact, stronger. This is kind of an important point, as it exposed German National Socialist Democratic Worker's Party as a bad economic manager, which you might think would be an important point that our larger learned and semi-learned public sphere might absorb as a counterpoint to the idea that authoritarian regimes at least have the advantage that they manage the economy better.
It doesn't, I think because 1939 was over too quickly. At the time, it may have happened day by day, just like any other year, but, in retrospect, we're just galloping through to get to the cool part, with dive bombers. It's a pretty common thing. Try to find a history of the Thirty Years War that spends as much time on Prince Thomas of Savoy as it does on Count Mansfeld, or a review of the Italian Wars that makes the War of the League of Cambrai as big a deal as the "descent on Italy" way back in 1494.
So: 1939, slowly.