- Beginnings -

North Korea's nuclear ambitions date back to the end of the Korean War in a stalemate in 1953.

In the 1960s, Pyongyang receives nuclear technology and hardware from the Soviet Union -- a key Cold War ally -- to create a nuclear energy programme.

By the 1980s, its scientists are believed to be working on a clandestine nuclear weapons programme, having already reverse-engineered missiles from a Soviet-era Scud.

- Longer range -

It carries out its first test of Scud-style Hwasong missiles in 1984.

Starting in 1987, it begins developing longer-range missiles, including the Taepodong-1 (2,500 km) and Taepodong-2 (6,700 km).

The programme receives a major boost -- including possibly warhead design blueprints -- in the 1990s from rogue Pakistani nuclear scientist Abdul Qadeer Khan.

The Taepodong-1 is test-fired over Japan in 1998, but the following year Pyongyang declares a moratorium on such tests as ties with arch-foe the United States improve.

- 2006-13: Nuclear tests -

It ends the moratorium in 2005, blaming the "hostile" policy of US President George W. Bush's administration, and carries out its first nuclear test on October 9, 2006.

In May 2009, there is a second underground nuclear test, several times more powerful than the first.

Kim Jong Un succeeds his father Kim Jong Il -- who dies in December 2011 -- as leader of North Korea, and oversees a third nuclear test in 2013.

- 2016: Japanese waters reached -

There is a fourth underground nuclear test in January 2016, which Pyongyang claims is a hydrogen bomb.

In August, it launches for the first time a ballistic missile directly into Japanese-controlled waters. Later that month, it successfully test-fires another submarine-launched ballistic missile (SLBM).

There is a fifth nuclear test in September.

- 2017: 'Fire and fury' -

Between February and May, Pyongyang launches a series of ballistic missiles that land in the Sea of Japan, also known as the East Sea. It says the tests are drills for possible hits on US bases in Japan.

In May, Pyongyang says it has tested an intermediate-range ballistic rocket, the Hwasong-12, which flies 700 kilometres.

Two months later, North Korea announces it successfully tested on July 4 an inter-continental ballistic missile (ICBM) capable of reaching Alaska -- a gift for the "American bastards" announced on US Independence Day.

There is a second successful ICBM test later that month.

Then president Donald Trump threatens Pyongyang with "fire and fury" over its missile programme.

- 2017: Largest nuclear test yet -

North Korea conducts its sixth and largest ever nuclear test on September 3, 2017. Monitoring groups estimate a yield of 250 kilotons, 16 times the size of the US bomb that destroyed Hiroshima in 1945.

Later that month, it fires an intermediate-range missile over Japan.

Trump declares North Korea a state sponsor of terrorism and imposes fresh sanctions.

On November 29, Pyongyang launches a new Hwasong-15 ICBM, which it claims could deliver a "super-large heavy warhead" to anywhere on the US mainland.

Analysts voice scepticism that Pyongyang has mastered the advanced technology needed to allow the rocket to survive re-entry into the Earth's atmosphere.

- 2018: Detente -

On April 21 2018, Pyongyang says nuclear tests and ICBM launches will cease immediately and that its nuclear test site will be dismantled to "transparently guarantee" the end of testing ahead of a first meeting between Trump and Kim in Singapore in June.

- 2019-2021: New weapons, new tensions -

A second summit in February 2019 between Trump and Kim in Hanoi collapses.

Tensions mount again in 2021 with North Korea carrying out a number of high-profile weapons tests, including a claimed submarine-launched ballistic missile, a train-launched weapon, and what it says is a hypersonic glide missile.

- 2022: 'Monster' missile and 'preventive' policy -

On March 24, Pyongyang fires an intercontinental ballistic missile, which it claims is the new Hwasong-17, which analysts dubbed a "monster missile".

Washington and Seoul say it was actually an older weapon, a Hwasong-15.

Kim says in April he will rapidly accelerate the development of his nuclear arsenal, then in September, North Korea changes its laws to allow it to carry out a preventive nuclear strike, and declares itself an "irreversible" nuclear power.

On October 4, Pyongyang fires an intermediate-range ballistic missile over Japan for the first time in five years, prompting Tokyo to activate its missile alert system and issue a rare warning for people to take shelter.

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