Most did their own independent development.
Many countries have nuclear weapons today including the United States. China, North Korea, South Korea, and Japan also have nuclear weapons.
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the first five countries that were involved in nuclear weapons are as follows;United StatesGermanyGreat BritainRussiaArgentina
As of 2012, the countries with the most nuclear weapons, counting actively deployed and stockpiled ones, are, in order of most to least:RussiaUnited StatesFrancePeople's Republic of China (mainland)United KingdomPakistanIsraelIndiaNorth Korea
America has the most nuclear weapons
As the category for this question is "Nuclear weapons", I'm presuming it refers to nuclear arms.As of 2012, the three countries with the largest stockpiles of nuclear weapons are, in order from most to least:RussiaUnited StatesFrance
Most did their own independent development.
Pakistan has about 100 nuclear weapons.
Most countries have zero nuclear weapons.
No one. Most countries do not export nuclear weapons. Instead, the countries obtain (1) nuclear technology and (2) radioactive material and build it themselves.
Many countries have nuclear weapons today including the United States. China, North Korea, South Korea, and Japan also have nuclear weapons.
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Some of the countries have nuclear weapons because they use them as a defense mechanism. The nuclear weapons are intended to be used whenever there is a war.
Nuclear weapons are governed by international agreements such as the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), which aims to prevent the spread of nuclear weapons. Additionally, there are regional and bilateral agreements that regulate the use and possession of nuclear weapons among specific countries. Some countries also have domestic laws pertaining to nuclear weapons possession and testing.
the first five countries that were involved in nuclear weapons are as follows;United StatesGermanyGreat BritainRussiaArgentina
None. No nuclear weapons were used in Viet Nam.