Why did they invent the nuclear bomb?

Answer 1

The nuclear bomb was invented when it became known that Nazi Germany was actively experimenting with nuclear material to build a possible bomb. Albert Eienstein urged President Roosvelt via a letter signed by him that he the president seriously commence a project to build a nuclear bomb. The project was code named "Manhattan Project". Eventually, some of the same scientist that were in Germany were brought to US where with their help the first bomb was tested. I believe the site is known as Trinity, New Mexico.

besides this facts, Einstein left Germany when he saw the military type regime in schools on time not to fall in the hands of the nazi.

Leo Szilard invented the nuclear reactor and nuclear bomb in London in 1933, shortly after the neutron was discovered as an improved source of neutrons for experiments. He was also very aware of their potential destructive effects. He was not able to build either at the time because of lack of a suitable material.

Otto Frisch discovered that Uranium-235 fissioned when hit by a neutron, producing an excess of neutrons in Berlin in 1938. This was the first material found that made Szilard's invention practical, but it is a very rare isotope and expensive to concentrate.

Szilard wrote the letter to FDR in 1942, but had Einstein sign it because his name and reputation were well known. Had Szilard signed it himself FDR might not have seen the significance and done nothing!

Enrico Fermi built the first nuclear reactor in Chicago, IL in 1942. It had a peak operating power of half a watt.

Los Alamos labs built the first nuclear bomb in Los Alamos, NM in 1945. It was tested at Trinity site, NM on July 16, 1945 with a yield of about 20KTons of TNT.

Answer 2

They invented the nuclear bomb to be the ultimate weapon of mass destruction. It was invented by a group of scientists. This group, ironically, included Einstein until he died and was replaced.