(People talk of the Warsaw-Ghetto uprising as being between April 19, 1943-May 16, 1943. In fact, the first active armed resistance to the deportation of Jews for extermination from the Warsaw Ghetto took place on January 18, 1943)
“Between July 22 and September 12, 1942, the German authorities deported or murdered around 300,000 Jews in the Warsaw ghetto. SS and police units deported 265,000 Jews to the Treblinka killing center and 11,580 to forced-labor camps. The Germans and their auxiliaries murdered more than 10,000 Jews in the Warsaw ghetto during the deportation operations. The German authorities granted only 35,000 Jews permission to remain in the ghetto, while more than 20,000 Jews remained in the ghetto in hiding. For the at least 55,000-60,000 Jews remaining in the Warsaw ghetto, deportation seemed inevitable.
In response to the deportations, on July 28, 1942, several Jewish underground organizations created an armed self-defense unit known as the Jewish Combat Organization (Zydowska Organizacja Bojowa; ZOB). Rough estimates put the size of the ZOB at its formation at around 200 members. The Revisionist Party (right-wing Zionists known as the Betar) formed another resistance organization, the Jewish Military Union (Zydowski Zwiazek Wojskowy; ZZW). Although initially there was tension between the ZOB and the ZZW, both groups decided to work together to oppose German attempts to destroy the ghetto. At the time of the uprising, the ZOB had about 500 fighters in its ranks and the ZZW had about 250.
While efforts to establish contact with the Polish military underground movement (Armia Krajowa, or Home Army) did not succeed during the summer of 1942, the ZOB established contact with the Home Army in October, and obtained a small number of weapons, mostly pistols and explosives, from Home Army contacts.
In October 1942, SS chief Heinrich Himmler ordered the liquidation of the Warsaw ghetto and deportation of its able-bodied residents to forced labor camps in the Lublin District of the Generalgouvernement. In accordance with this order, German SS and police units tried to resume mass deportations of Jews from Warsaw on January 18, 1943. A group of Jewish fighters, armed with pistols, infiltrated a column of Jews being forced to the Umschlagplatz (transfer point) and, at a prearranged signal, broke ranks and fought their German escorts. Most of these Jewish fighters died in the battle, but the attack sufficiently disoriented the Germans to allow the Jews arranged in columns at the Umschlagplatz a chance  to disperse. After seizing 5,000-6,500 ghetto residents to be deported, the Germans suspended further deportations on January 21.
Encouraged by the apparent success of the resistance, which they believed may have halted deportations, members of the ghetto population began to construct subterranean bunkers and shelters in preparation for an uprising should the Germans attempt a final deportation of all remaining Jews in the reduced ghetto.” 
“On January 18, 1943, after almost four months without deportations [a brief respite], the Germans suddenly entered the Warsaw Ghetto intent upon further roundups. Within hours, some 600 Jews were shot and 5,000 others removed from their residences. The Germans expected no resistance, but the action was brought to a halt by hundreds of insurgents armed with handguns and Molotov cocktails.” 
(A year later — June 6, 1944 — the Allies invaded Normandy. Less than a year after D-Day — May 7, 1945; almost two years to the day from when Mordecai Anielewicz had died fighting — the Nazis formally surrendered and WWII in Europe was over. This was only 2 years after the Nazi destruction of the Warsaw Ghetto.)
 picture is of Mordecai Anielewicz, a leader of the armed resistance. He died fighting around 5 months later, on May 8, 1943, at age 24).