The Holocaust was a genocide that took place during World War II, targeting primarily European Jews. It was orchestrated by Adolf Hitler and the Nazi regime, resulting in the systematic persecution and murder of approximately six million Jews. The world came to know about the Holocaust through various means, including eyewitness accounts, documentary evidence, and the liberation of concentration camps.

Background:
- Adolf Hitler rose to power in Germany in 1933, establishing a fascist regime and implementing anti-Semitic policies.
- The Nazis believed in the superiority of the Aryan race and propagated hatred towards Jews, blaming them for Germany's problems.

Implementation of the Holocaust:
- The Nazis implemented a series of discriminatory laws, stripping Jews of their rights and property.
- In 1939, Germany invaded Poland, starting World War II and providing a pretext for further persecution.
- The systematic killing of Jews began with mass shootings in Eastern Europe, carried out by special units called Einsatzgruppen.
- However, the Nazis soon realized that mass shootings were inefficient and psychologically damaging for the perpetrators, leading to the development of extermination camps.

World becoming aware of the Holocaust:
- Eyewitness accounts: Some Jews managed to escape the Nazis and shared their horrifying experiences with the world.
- Underground resistance movements: Jewish and non-Jewish resistance fighters smuggled out information and documented the atrocities.
- Concentration camp survivors: As Allied forces advanced, they began liberating concentration camps, revealing the extent of the Holocaust.
- Nuremberg Trials: After the war, the Allies held trials to prosecute Nazi leaders, which provided further evidence and publicized the Holocaust.

Post-war efforts:
- The United Nations established the International Military Tribunal to address war crimes, including those related to the Holocaust.
- Survivors and organizations like the Jewish Displaced Persons (DP) camps worked to preserve the memory of the Holocaust.
- Scholars, historians, and survivors began documenting and researching the Holocaust, ensuring that the truth was not forgotten.

Legacy:
- The Holocaust stands as one of the darkest chapters in human history and serves as a reminder of the dangers of hatred, prejudice, and discrimination.
- It prompted the establishment of the State of Israel as a homeland for Jewish survivors.
- Efforts like Holocaust education and remembrance ensure that the world acknowledges and learns from this horrific event, striving to prevent future genocides.

In conclusion, the Holocaust was a brutal genocide committed against Jews during World War II. The world learned about this atrocity through a combination of eyewitness accounts, liberation of concentration camps, documentation by resistance movements, and subsequent trials and research. The Holocaust's impact on history and the collective memory of humanity cannot be understated.