The only nation to use nuclear weapons in combat: The United States
The nation that developed these fission weapons: The United States
Fission refers to the splitting of an atom’s nucleus by a penetrating neutron. These are atomic bombs that use plutonium or uranium.
The nation that developed thermonuclear weapons: The United States
These are H-bombs that operate under nuclear fusion when hydrogen atoms are merged or fused together. It does require, however, an atomic explosion that precedes the fusion to create the temperatures necessary for such an event. An H-bomb actually is a little A-bomb, followed by an H-bomb.
The nation that invented the monstrous MIRVing. That is multiple nuclear bombs or actually reentry vehicles on top of a missile that separates in space and travel to separate targets: The United States
The only nation besides North Korea to formally break and terminate a nuclear treaty: The United States.
The U.S. broke the A.B.M. treaty which brilliantly limited national defence against nuclear weapons to constrain the arms race in which the U.S. and the U.S.S.R. would build more offensive weapons to saturate a possible defence. By avoiding a national defencive system, it put a damper, at least in theory, in creating more offensive systems. The U.S. broke this so it could deploy a first-strike capability against emerging nuclear states that resist American imperialism. By creating an A.B.M. system in Alaska, which won't work, they hope to interdict nuclear weapons from say a North Korea or Iran, but I think the game plan is to develop a first-strike capability if these nations go nuclear.
A first-strike capability means launching a nuclear attack without retaliation. The U.S. according to Seymour Hersh is planning a tactical nuclear assault on Iran and it would not surprise me if this country does indeed initiate nuclear war in the not too distant future. This is our fate unless somehow the nation can be transformed by regime change or some emerging nation than can deter and contain American aggression. I don't see a willingness on the part of the U.S. to end its Cold War reliance upon military force and imperial efforts to maximise power. Perhaps if we are fortunate, we will encounter some developing nation that can contain the unbridled and frankly out-of-control militarism that creates perpetual war for perpetual greed for perpetual empire that will lead to national destruction and devastation.
Tactical weapons, a real immoral term, is the notion that nukes can be used in a controlled manner on a battlefield. Nuclear artillery, SRAMs from aircraft that travel a short distance, nuclear bunkerbuster weapons that travel through the surface of the Earth and have a delayed detonation in subsurface fashion. This is what the U.S. is developing as 45-48 million Americans have no health insurance.
The government is not too terribly concerned about the health and safety of its citizens but is convinced national greatness is a good quality and that it can be defined primarily by superior firepower. Such is the state of American civilisation with its utter lack of realism whereby the national interest is defined not by a sensible pursuit of power but in an indiscriminate manner that destroys our domestic agenda and reduces our national character to torture, belligerent speech and socipathic pursuit of global domination.