It's so sad and fascinating to learn about the Holocaust. There are so many lessons, all at the cost of death, that we ignore. I think it difficult to fault people (including myself) who never properly learned the history and implications of the Holocaust. How can you blame people who don't remember when they never knew it in the first place? It brings to mind Ray Bradbury's wonderful Fahrenheit 451:

"Every hour so many damn things in the sky! How in hell did those bombers get up there every single second of our lives! Why doesn't someone want to talk about it? We've started and won two atomic wars since 1960. Is it because we're having so much fun at home we've forgotten the world? Is it because we're so rich and the rest of the world's so poor and we just don't care if they are? I've heard rumours; the world is starving, but we're well-fed. Is it true, the world works hard and we play? Is that why we're hated so much? I've heard the rumours about hate, too, once in a long while, over the years. Do you know why? I don't, that's sure! Maybe the books can get us half out of the cave. They just might stop us from making the same damn insane mistakes!"

Anyway, this is from the linked article Holocaust Resistance: The Warsaw Ghetto Uprising (April 19 - May 19, 1943):

In 1942, Hitler decided to liquidate the ghettos and, within 18 months, had the more than two million Jews who’d survived the ghettos deported to death camps.

The Germans ordered the Jewish “police” in the Warsaw ghetto to round up people for deportation. Approximately 300,000 men, women, and children were packed in cattle cars and transported to the Treblinka death camp where they were murdered. This left a Jewish population of between 55,000 and 60,000 in the ghetto.

Mordecai Anielewicz

In April 1943, the Jews learned the Germans planned to deport all the people who remained in the Warsaw ghetto to Treblinka. A group of mostly young people formed an organization called the Z.O.B. (for the Polish name, Zydowska Organizacja Bojowa, which means Jewish Fighting Organization). The Z.O.B., led by 23-year-old Mordecai Anielewicz, issued a proclamation calling for the Jewish people to resist going to the railroad cars.

In January 1943, Warsaw ghetto fighters fired upon German troops as they tried to round up another group of ghetto inhabitants for deportation. Fighters used a small supply of weapons that had been smuggled into the ghetto. After a few days, the troops retreated. This small victory inspired the ghetto fighters to prepare for future resistance.

...After the January battle, the Jews spent the following weeks training, acquiring weapons, and making plans to defend of the ghetto. The Germans also prepared for the possibility of a fight. On the eve of the final deportation, Heinrich Himmler replaced the chief of the SS and police in the Warsaw district, Obergruppenfuhrer Ferdinand von Sammern-Frankenegg, with SS und Polizeifuhrer (SS and Police Leader) Jurgen Stroop, an officer who had experience fighting partisans.

The ghetto fighters were warned of the timing of the final deportation and the entire Jewish population went into hiding. On the morning of April 19, 1943, the Warsaw ghetto uprising began after German troops and police entered the ghetto to deport its surviving inhabitants. Seven hundred and fifty fighters armed with a handful of pistols, 17 rifles, and Molotov cocktails faced more than 2,000 heavily armed and well-trained German troops supported by tanks and flamethrowers.

After the Germans were forced to withdraw from the ghetto, they returned with more and more firepower. After several days without quelling the uprising, the German commander, General Jürgen Stroop, ordered the ghetto burned to the ground building by building. Still, the Jews held out against the overwhelming force for 27 days. On May 8, the headquarters bunker of the ZOB at 18 Mila Street was captured. Mordecai Anielewicz and a large number of his colleagues were killed in the fighting, but several dozen fighters escaped through the sewers.

How incredibly sad. Sent shivers down my spine.