As tensions between America and North Korea simmer, politicians around the world have stepped into condemn Kim Jong-un’s threats of nuclear war.

“The North Korean regime is the cause of this problem and they must fix it,” the UK foreign secretary, Boris Johnson has said.

“The international community is shoulder to shoulder in ensuring North Korea stops its aggressive acts.”

But how did such an isolated and poverty-stricken country manage to get nuclear weapons in the first place?

Somehow, North Korea has obtained the money, knowledge and materials necessary to build missiles which it claims can reach American soil.

Cold War collaborations

To understand how North Korea got its nuclear weapons, we need to go back to the Second World War.

The whole Korean Peninsula had been under Japanese colonial rule since 1910. But when the US dropped atomic bombs on Hiroshima and Nagasaki in 1945, Japan surrendered and Korea was ‘liberated’.

The peninsula was divided in two: the US controlled the south, while the Soviet Union controlled the north, with former Soviet soldier Kim Il-sung as its administrative leader.

Both north and south claimed power over the whole area, which ultimately led to the Korean War in 1950. As fighting broke out, US President Truman warned that the use of an atomic bomb was under “active consideration”.

In the end, this threat was not carried out, but both North and South Korea were left in ruins by the war.

In North Korea, more than a million people were killed or unaccounted for, while many more were injured.

When the war ended, the two sides signed an armistice and Kim Il-sung began consolidating his power in North Korea. He started a dynasty – succeeded by his son, and then his grandson, Kim Jong-un, who is the current leader.

But the tensions with South Korea and America remained.

During the Cold War, North Korea began working with Soviets over its nuclear capabilities. They signed a joint research agreement in 1956 and, for years, Korean scientists were invited abroad for training.

Meanwhile, the US were well ahead of the game. By the early 1960s, it had around 600 nuclear weapons positioned below the border in South Korea.

North Korea, on the other hand, had only progressed to conducting basic experiments. If it was to get nuclear weapons, help from other countries would be essential.

Not long after the Soviet help began, China also got in on the act. For instance, they helped with a geological survey to find uranium in North Korea, revealing huge deposits across the country.

The Pakistan allegations

By the 1990s, North Korea pulled out of the nuclear non-proliferation treaty and started using more covert methods to develop its technology.

Documents published by the Washington Post in 2011 appeared to suggest that North Korea managed to bribe top officials in Pakistan’s military to share their country’s nuclear secrets.

One insider, Abdul Qadeer Khan, claimed that he had personally transferred more than $3 million to corrupt officers.

Huge amounts of cash and jewels were apparently transferred inside cardboard boxes of fruit, in return for sensitive information.

The Pakistani officials have denied the claims, but US intelligence officials believe the evidence is authentic.

Khan says that he was involved in selling components to Iran and Libya, as well as North Korea. But he claims he was acting on behalf of other senior leaders in Pakistan.

The British connection

In order to transfer money, information and components for nuclear weapons, North Korea uses a complicated web of secretive front companies across the world, according to a UN report.

And that includes links to Britain. One such company that was alleged to be involved was finally closed down in 2016, after operating for 11 years.

The Korea National Insurance Corporation was registered in a detached house in the leafy suburbs of south London.

But reports claimed it was secretly channeling up to £33 million a year to Kim Jong-un.

Authorities linked the firm to a secretive arm of the North Korean government which generates “revenues for the leadership” by managing slush funds.

North Korean officials denied the allegations. An anonymous spokesperson for the embassy in London told the Mail on Sunday: “The EU is making baseless assumptions about KNIC. The company and its workers have been made scapegoats. KNIC has not funded the nuclear programme.”

However, the British connection doesn’t end there.

When North Korea launched its Unha-3 rocket in 2012, South Korea managed to recover some of the debris and allowed UN investigators to examine it.

They found parts that had been manufactured across the world, including Switzerland, the US and the UK.

Most of these parts were not specifically listed as “prohibited items” for trading – and the manufacturers were probably unaware that they would be used to help develop North Korea’s nuclear programme.

But the UN said the discovery showed that the regime was able to assemble complex missile systems using “globally sourced components”.

So who exactly were these British manufacturers?

FactCheck has obtained letters sent between British government and the UN, showing that authorities managed to identify three different businesses.

The companies have never been named because government investigators agreed to grant them anonymity.

Their names have been redacted throughout the documents, which were released to FactCheck under the Freedom of Information Act.

The letters suggest that components were sold through a complex chain of companies, before finally ending up in North Korea. Many of them, it seems, were transported via firms in China.

This was not a one-off, either. Parts made by at least one of these British companies were found yet again, following another North Korean missile test in 2016.

This time, however, they had come via a different chain of companies.

The pressure transmitter on the left was found in North Korea’s missile test in 2012; the one on the right came was used in 2016. But both were originally manufactured in the UK.

According to the letters we’ve seen, the British companies were cleared of any wrongdoing.

But it has proved difficult for investigators to find out exactly where in the transaction chain the problem lies.

Ukrainian links?

Classified assessments and analysis have recently suggested that North Korea bought the engines for their rockets off a black market, which may link back to a factory in the Ukraine.

Reports claim the factory used to have ties with Russia’s missile programme.

Michael Elleman, a missile expert at the International Institute for Strategic Studies, said: “The big question is how many they have and whether the Ukrainians are helping them now.”

But the evidence here is not clear. Yuzhmash, the state-owned Ukrainian aerospace company concerned, has disputed the claim – as have the Ukrainian government as well as a US intelligence official.

Elleman explained his analysis saying that the type of liquid-propellant engines used by North Korea recently were based on designs developed under the Soviet Union, and likely came from the Ukrainian factory.

“We’ve seen it there,” he said. “So that’s the most likely source.”

However, an unnamed US intelligence official told CNN: “We have intelligence to suggest that North Korea is not reliant on imports of engines – instead, we judge they have the ability to produce the engines themselves.”

But the Ukrainian link doesn’t end there. CCTV footage released by the country’s security services in August reportedly showed two North Korean spies photographing what they thought were designs for nuclear missiles. It was actually an elaborate sting operation to catch the secret agents.

Ukrainian officials used this footage to argue that they would have successfully intercepted any attempt by North Korea to obtain missile technology from them.

Whoever is right about Ukraine’s links with North Korea’s nuclear missile programme, there is no doubt that a range of countries around the world have been essential for acquiring the the necessary materials and cash.

Despite efforts from the international community, it seems the flow of resources has continued.

Evading sanctions

According to the UN, North Korea has increasingly tried to circumnavigate rules and sanctions by using secretive organisations and criminal groups.

The UK government already has sanctions in place against 55 organisations and 100 individuals. But it seems there are many more who have slipped under the authorities’ radar.

Particularly useful to the North Korean regime are many of the world’s secretive tax havens, which have allowed financial paper trails to be buried.

For instance, a firm called DCB Finance Ltd was registered in the British Virgin Islands by a former British banker, Nigel Cowie.

But leaked documents seen by the Guardian suggest it was actually front company for Daedong Credit Bank, which has allegedly been used to help finance and expand North Korea’s nuclear weapons programme.

Nigel Cowie’s lawyer told the Guardian that DCB Finance Ltd was used for “legitimate business”, adding that Cowie was “unaware of any transactions being made with any sanctioned organisation or for any sanctioned purpose, during his tenure”.

However, the US issued sanctions against his company in 2013, claiming it was used by Daedong Credit Bank “as a means to avoid scrutiny”.

Elaborate secrecy is not uncommon. In February, the UN said North Korea’s evasion techniques were “increasing in scale, scope and sophistication”.

It said: “Diplomats, missions and trade representatives of the Democratic People’s Republic of Korea systematically play key roles in prohibited sales, procurement, finance and logistics.”

According to one account, the UN suspects North Korea of shipping materials from countries including China, Greece, Turkey, Taiwan, Vietnam, Malaysia, the United Arab Emirates, Cyprus, Liechtenstein, the Cayman Islands, the Philippines, Mauritania, Singapore.

The sheer number of countries, companies and individuals tied up in it all makes preventing the flow of resources a near impossible task.

But one thing seems certain: North Korea wouldn’t be able to make its nuclear weapons without help from the outside world.