Choosing history’s most momentous developments is tricky for all sorts of obvious reasons. But there is little doubt that the Hitler-Stalin Pact (more accurately the Molotov-Ribbentrop Non-Aggression Pact named for its actual signatories) signed on this day 74 years ago is among them. It facilitated the almost immediate invasion of Poland by Germany (followed by the secretly-agreed-upon occupation of Eastern Poland by the USSR) and thus the beginning of World War II. It produced the landscape for the Holocaust, and the wider calamity of the vast slaughter of people in the regions over which Nazi Germany and the Soviet Union ultimately battled (called the “Bloodlands” in Timothy Snyder’s brilliant and disturbing book of that same name). And it undermined, perhaps permanently, the credibility of Great Power diplomacy as an instrument for preventing war and managing peace.

There are many theories, some overlapping, for why this astounding development (astounding at the time and only a bit less astounding today) occurred. Some blame the concessions to Germany made by England and France at Munich for convincing Stalin the West wanted to maintain Hitler as an anti-Soviet bulwark. Some blame Stalin for so devastating the Soviet armed forces during the Great Purge that the country had to sue for peace until preparedness could be restored. Some even blame Poland for resisting Soviet demands that its forces be allowed to cross Polish borders in the event of a German attack, which ultimately frustrated efforts to secure a Russian alliance with England and France. The most common explanation is probably that Hitler and Stalin were united in cynical disregard of their own ideological professions, and shared the ability to strike an audacious alliance without fear of domestic repercussions. It’s almost certainly true that both dictators understood they would eventually go to war with each other, and had varying reasons for postponing war’s advent (Stalin, of course, fatally miscalculated the respite he had secured, and famously disregarded the mounting evidence supplied by his own diplomats and spies that war was imminent in 1941).

In any event, the Pact caught the Western Allies off guard, and made Hitler’s 1939 and 1940 victories immensely easier. It also produced a psychological crisis among Communists outside the USSR, who were suddenly expected after years of warning about the dangers of fascism to treat the war against Hitler as an “imperialist struggle” in which no genuine progressive should participate.

Critics of the great folk singer Pete Seeger often point to his (and the Almanac Singers’) 1941 antiwar album, Songs for John Doe, as the primary evidence of his subservience to Soviet foreign policy, particularly since copies of the album were suppressed after Germany invaded the Soviet Union. Seeger never hid the fact that he (and Woody Guthrie) “flip-flopped” on the war, and I’m sure he would have argued that it was the strategic situation, not just the Party Line, that changed his mind. But at any event, this cut from Songs For John Doe is a reminder of that strange period of U.S. history when Communists and the America First Committee–not to mention dominant forces in both the major political parties–did not want to fight The Good War.

Ed Kilgore

Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.