Long-time readers know that I love "best _____ of all-time" lists and questions. Arriving at a precise answer for a question like "What's the best movie ever?" is an impossible task but it's lots of fun to argue about it. Over at the Economist's Intelligent Life Magazine, they've taken up the most preposterous (by which I mean awesome) "best of" question I've ever heard: What was the most important year ever?
But alongside 1776, we must include 1945. The atomic bombs alone changed the world's sense of itself, never mind the final defeat of Nazi Germany, whose attempted genocide of the Jewish people remains the single most important moral fact of modern times, the one that has done most to change the way we think. It was the year when American hegemony in the West was established and when the long Stalinist bondage of eastern Europe began, and when India took decisive steps towards independence.
Update: Several more Economist writers have weighed in. Their choices: 5 BC (birth of Jesus), 1204 (Christianity divided by Crusades), 1439 (Gutenberg's press), 1791 (invention of telegraph), and 1944 (beginning of worldwide ideological war). Don't like those choices? Vote for your own.