On this date in history in 1945, the allied bombing attack on Dresden commenced. Between February 13 and February 15, 1,300 allied bombers dropped 3,900 tons (that's 7,800,000 pounds) of explosives and incendiaries on the city, creating a firestorm in the center of the city that completely detroyed that section; it also killed somewhere between 24,000 and 40,000 civilians--the greatest number of civilians killed in an attack until August of that year (Hiroshima and Nagasaki).
Did that attack constitute a war crime? Since the victors of wars define that, and rarely charge themselves, that answer is self-evident. There were truth-tellers who survived that attack, however, including a young American prisoner-of-war, kept safe in an underground slaughterhouse by his captors.
That witness went on to write a number of well-received books, including the one adapted into the movie above.