Here are two links each with a detailed chronology of the history of nuclear weapons. This can teach a lot about the motivations behind various actions, sheding more light on present day events. More accounts may be found in the Policy & Law section.

The Atomic Archive (abreviated history)
Nuclearfiles.org

The Trinity Test. The first atomic explosion took place on July 16, 1945, at 5:29:45 AM, Alamogordo, New Mexico, USA.