The Halocaust
The holocaust.
Holocaust is the name.
The mass killings took place between 1941 and 1945.
Who could have actually stopped the Holocaust and how? Many other countries were already at war with Germany when the systematic mass killings began. Please have a look at the related question.
The Final Solution refers to Hitler's intention to eliminate the Jews from Europe, which for a while involved four deportation plans which was eventually discarded and then became mass killings of Jews which resulted in the final solution becoming the mean the mass murder of Jews in Europe.
If your question is referring to the mass murder of Jews, and others by the Nazis then it ended with the surrender of German forces to the United Nations in May 1945. However mass murder was not limited to the NAZIS. Rwanda, Sudan, Soviet Union, Cambodia, Yugoslavia, just to name a few have all had governments that practiced mass killings.
The Final Soution was decided at the Wansee Conference, this idea of the Final Solution started the mass killings in the Concentration Camps.
It led to the mass removal of Jews to Nazi concentration camps.
The SS and Nazi leaders meet at Berlin in a suburd of Wansee to make plans for the starting of mass killings of the Jews aka "Final Solution" or "the Jewish problem."
In Rwanda.
The mass media killings in the Philippines attracted reactions from all over the world. These were regarded as extra-judicial killings that saw many journalists lose their lives in 2008.
If you mean the WWII holocaust, mainly Nazi Germany. There were other mass killings around that time: Japan in China, and Stalin in the Soviet Union.