The first nuclear explosion in history took place in New Mexico, at the Alamogordo Test Range, on the Jornada del Muerto (Journey of Death) desert, in the test named Trinity. This test was intended to prove the radical new implosion weapon design that had been developed at Los Alamos during the previous year. This design, embodied in the test device called Gadget, involved a new technology that could not be adequately evaluated without a full scale test. The gun-type uranium bomb, in contrast, was certain to be effective and did not merit testing. In addition, since no nuclear explosion had ever occurred on Earth, it seemed advisible that at least one should be set off with careful monitoring to test whether all of the theoretical predictions held.
(This has the the original sound so you might want to turn your speakers down.)
This kinda speaks for itself.
The Crossroads Series tests were the first nuclear explosions since World War II, and the first nuclear weapon tests since Trinity. These were the first "weapons effects" tests ever conducted - tests designed specifically to study how nuclear explosions affect other things - rather than tests of the behavior of a weapon design (as was Trinity). The purpose of the tests was to examine the effects of nuclear explosions on naval vessels, planes, and animals.
The next two videos are the largest nuclear weapon ever.
The bomb was tested on October 30, 1961, in Novaya Zemlya, an archipelago in the Arctic Sea. Tsar Bomba' (Царь-бомба, literally "Emperor Bomb") is the Western name for the RDS-220 (codenamed "Ivan" by its developers), which was the largest, most powerful nuclear weapon ever detonated. Developed by the Soviet Union, the bomb was originally designed to have a yield of about 100 megatons of TNT, however that was reduced by half in order to limit the amount of nuclear fallout that would result.