From 1945 until the late 1970s or early 1980s the United States always had the most nuclear weapons. After then the USSR/Russia has had the most nuclear weapons.
Russia
The country with the biggest stock of nuclear weapons, and hence, the biggest productor is the Russian Federation. They have over 12,000 nuclear warheads.
According to my research the most weapons country is the United States currently owns 9,600 nuclear weapons, while Russia currently owns 16,800. But Russia actually always had more nuclear weapons than the United States.
Most countries have zero nuclear weapons.
Because nuclear weapons are the most deadly of all weapons and can kill hundreds of thousands of people at once. Also, people will always get suspicious if a country is secretly making nuclear weapons e.g. Iran and USA. IF one country wants to build nuclear weapons then their neigh ours would want to too
The Russian Federation has the most nuclear weapons as of 2010 (Se Guiness World Records Book 2010
America has the most nuclear weapons
Russia
On the NPT record, the most recent entry I can see is for Montenegro, 3 June 2006.
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
In the most basic sense, proliferation of nuclear weapons is the spread of nuclear weapons and weapons usable technology in the world. In a much broader sense, it refers to the acquiring of capability to produce nuclear weapons, or weapons-grade nuclear material (high-enriched uranium, plutonium) by states previously not possessing them.