April 20th is Hitler's Birthday. In 1943, Heinrich Himmler wanted to give Hitler a particularly nice birthday present. He decided that in honor of Hitler's birthday he would eliminate the entire Jewish Ghetto of Warsaw, which had been causing trouble in the early months of 1943.

Instead, the Jews of Warsaw gave Hitler a present that he certainly didn't want: months of armed rebellion that DEFEATED the German army repeatedly and wasn't completely crushed until October 1943, though major combat operations, to borrow a phrase, were completed around May. Including the periods of more sporadic fighting, this resistance lasted far longer than the German take over of Poland as a whole, which took scarcely one month. It is pointed out in Melvin Konner's book Unsettled that the Warsaw Ghetto uprising, largely fought by Jews but with some Polish uprisings occurring at the same time and inspired by the Jewish uprising, also lasted longer than the time it took Germany to defeat France, though again you have to include the period of more sporadic fighting as well as the main combat.