Isobars are atoms that have same atomic mass but different atomic number. They have different atomic numbers because they have different numbers of protons. They have the same atomic mass because they have just enough neutrons to make the same total of nucleons. Isobars occur at different places in the Periodic Table.
The Holocaust (also called Ha-Shoah in Hebrew) refers to the period from January 30, 1933 - when Adolf Hitler became chancellor of Germany - to May 8, 1945, when the war in Europe officially ended.
WWI began in 1914 with the assassination of the Austrian Archduke Ferdinand in Croatia and ended with the treaty of Versailles in 1918. WWII began in Europe in 1939 with the invasion of Poland and earlier in the Pacific with the Japanese invasion of China.