Nuclear blackmail

Nuclear blackmail is a form of nuclear strategy in which an aggressor uses the threat of use of nuclear weapons to force an adversary to perform some action or make some concessions. It is a type of extortion that is related to brinkmanship.
Effectiveness.
Nuclear blackmail is generally regarded as ineffective against a rational opponent that has or is an ally of a power with assured destruction capability. If both states have nuclear weapons, nuclear blackmail becomes a threat of conflict escalation. In that situation if the opponent refuses to respond, one's choices are surrender or suicide. During the Cold War, the explicit threat of nuclear warfare to force an opponent to perform an action was rare since most nations were allies of the Soviet Union or the United States.
History.
In 1950, US President Harry Truman publicly stated that the use of nuclear weapons was under "active consideration" against Communist Chinese targets during the Korean War.
In 1953, US President Dwight Eisenhower threatened the use of nuclear weapons to end the Korean War if the Communist Chinese refused to negotiate.
To support the continued existence of the government of the Republic of China, the United States issued several nuclear threats against the Communist Chinese in the 1950s to force the evacuation of outlying islands and the cessation of attacks against Quemoy and Matsu.
Declassified documents from the British National Archives indicate that the United Kingdom considered threatening Communist China with nuclear retaliation in 1961 if they militarily reclaimed Hong Kong.
Ali Magoudi, a psychoanalyst of French President François Mitterrand, claimed that British Prime Minister Margaret Thatcher had threatened nuclear war against Argentina during the 1982 Falklands War to procure codes from France to disable Argentina's French-made missiles. This claim has not been confirmed by either the French or British governments.
In 1981, the US Department of Energy said there had been 75 cases of nuclear blackmail against the US but only several were serious attempts.
In 1991, Israel threatened Iraq with a "nuclear counter-response" if there was an attack using chemical weapons during the Gulf War. 
In 2002, the George W. Bush administration declared that it was prepared to strike with nuclear missiles against Iraq if biological or chemical weapons were used against American troops or their allies during the Iraq War. 
On January 2, 2018, US President Donald Trump threatened North Korea that the US has much more nuclear firepower than North Korea in response to a press release stating that a "nuclear button is on Kim Jong-un's desk at all times."
In fiction.
Nuclear blackmail, typically by a supervillain rather than a state, has been frequently employed as a plot device in spy fiction and action films. Since such a scheme appeared in the film "Thunderball", the trope has been particularly associated with the "James Bond" series and the TV series "24". The notion of a supervillain threatening world leaders with a nuclear device has since become a cliché, and has been parodied in Charles K. Feldman's "Casino Royale", "", "The Simpsons" episode "You Only Move Twice", and other espionage spoofs.