United States
The United States was the first country to develop nuclear missiles. It happened during World War II when it collaborated with the United Kingdom and Canada in the Manhattan Project as it raced against Nazi Germany to be the first to have the bomb.
It tested its first nuclear weapon in 1945 in what it dubbed as “Trinity.” It then used the weapon twice against Japan.
In 1952, it tested the hydrogen bomb in “Ivy Mike,” before following it up with a deployable weapon in 1954's “Castle Bravo.” It is a signatory to the NPT. It has the most number of active nuclear weapons at 2,150.