For decades, the Democratic People's Republic of Korea - more commonly known as North Korea - has been one of the world's most secretive countries.
Its government doesn't like people from outside the country going there and finding out what's going on.
It shares a border with a country called South Korea - and the two countries have not gone on with each other for a long time.
A North Korean leader has not stepped foot in South Korea for 65 years and the leaders of the countries have not met for 10 years.
But that has just changed. Kim Jong-un has now met with the president of South Korea, Moon Jae-in, at the border between the two countries.
In order to understand why this is so important, we need to look back over the last few decades at the history of this secretive country.
When was North Korea created?
North Korea was formally created on 9 September 1948, following the end of the Second World War, along with another country called South Korea.
The political differences between the two rival states led to the outbreak of a horrific war in 1950, which lasted three years.
Since then, North Korea and South Korea have been enemies.
Who's in charge?
Since 1948, North Korea has been ruled by three men from the same family.
Kim Il-sung was the country's first supreme leader, who was in charge until his death in 1994.
Control passed next to his son Kim Jong-il, who held power for 17 years.
In 2011, North Korea announced Kim Jong-il's son, Kim Jong-un, as its new leader.
Around a million people gathered in the capital city, Pyongyang, to hear the announcement.
What is life like there?
North Korea is home to more than 24 million people, who live under a form of communist rule, which strictly controls all areas of daily life.
People have to ask permission to travel around and it's difficult for visitors to enter the country too.
All TVs and radios are tuned to state channels and people caught listening to foreign broadcasts face harsh punishments.
These controls mean that most North Koreans may have little or no idea of world events, or how their country is thought of by the outside world.
Most North Koreans are extremely poor with things like fridges, washing machines, and even bicycles, hard to come by.
Many people rely on aid agencies, such as the United Nations, to provide food because there is not enough in the country to eat.
However, North Koreans who demand more from their government, demand a change in leadership, or those that just try to escape, are brutally punished and sometimes killed.
An Amnesty International report estimates that hundreds of thousands of people have been put in prison and labour camps because they have disagreed with the government.
North Koreans seem to cheer and praise their leader at big public events but it's difficult to know the reasons for this because it's not possible to speak freely to people living there.
The North Korean Government says it's because Kim Jong-un is very popular with his people.
From an early age, North Koreans are taught that their leaders are like all-powerful gods.
But others argue that people could be cheering Kim because they are worried that they would get in serious trouble if they didn't.
Why are people worried about North Korea?
North Korea has been trying to make nuclear missiles - powerful bombs that can cause devastating damage - which one day might be able to hit targets in the USA.
It wasn't believed that it was building any missiles that could travel to and strike the UK, which is around 8,400 kilometres away.
US President Donald Trump sent warships and submarines to South Korea, a country which America has supported for a long time, to try to get Kim Jong-un to stop his weapon-building plans.
In August 2017, North Korea fired a missile, which is able to carry weapons, over northern Japan for the first time. It then crashed into the sea.
Two weeks later the country fired a second missile over Japan which flew higher and further than the first one. It too landed in the sea.
Japanese Prime Minister Shinzo Abe called the action a "serious" threat to his country.
In November 2017, North Korea said it had successfully tested a new type of missile that could reach the whole of the United States.
The Hwasong-15 missile, described as the country's "most powerful", landed in the sea.
He also said a nuclear testing site in the north of the country will be shut down.
President Trump tweeted that the announcement is "good news" for the world.
At the start of 2018, Mr Kim ended up in another war of words with President Trump.
Mr Kim made his New Year address saying he always has his nuclear launch button on his desk. Mr Trump responded by saying his button was bigger and the weapons he had were bigger and more powerful.
There have been many arguments between the US and North Korea in the past and, although they've never been friends, things have always been worked out to stop a war in the past.
Many people though that the relationship between America and North Korea was getting better as the two leaders planned to meet face to face.
It was a bid deal because no serving US president has ever sat down for talks with a North Korean leader.
But Donald Trump pulled out of the talks. He says it's because of 'tremendous anger' in a recent statement from North Korea and a series of "broken promises" from the North Korean capital Pyongyang.
President Trump said however that he was very much looking forward to meeting him 'some day'.
At the same time, efforts have been made by North Korea to start friendlier talks with its neighbour, South Korea.
Mr Kim had said he was open to communicating and, in January 2018, a secure phone line was reopened allowing the two governments to talk to one another.
It had been almost two years since this phone line was disabled on the orders of Kim Jong-un.
It came after the North Korean leader spoke of lowering tensions and of melting "frozen North-South relations".
Then, Mr Kim sent a team to the Winter Olympics in the South.
He said attending the games was "a good opportunity to show unity of the people" in North Korea.
South Korea and North Korea came together during the opening and closing ceremonies of the 2018 Winter Olympics in Pyeongchang.
Most recently in April 2018, the leaders of North and South Korea met at the border between the two countries for the first time in 10 years.
They have not held serious talks since December 2015, so this was a significant event.
Many people hoped that the talks between the two leaders could lead to peace between the countries.
Meanwhile talks between North Korea and the United States had still not happened.
At the end of May, President Trump pulled out of a meeting with Kim Jong-Un, which had been due to take place on the 12 June.
He said it was because of 'tremendous anger' in a recent statement from North Korea, and a series of "broken promises" from the North Korean capital Pyongyang.
But then on 2 June it was announced that the summit between President Trump and Kim Jong-un in Singapore was back on.
The news came after the North Korean envoy General Kim Yong-chol hand-delivered an unusually big letter from the North Korean leader to President Trump.
President Trump told reporters it was a "very interesting" letter - but later admitted that he hadn't yet read it.
Their meeting started with a handshake and there were just two translators in the room with them. Kim Jong-Un said it had not been easy to get to this stage and that "there were obstacles but we overcame them".
After the two leaders spent around 40 minutes discussing some of the issues between the two countries, they invited all their advisors to join them for lunch. The two countries then agreed a statement about what they want to do to improve their relationship.
Afterwards, as they both signed the joint statement in front of members of the media, President Trump said "we've had a really great time together".
Kim Jong-Un added that "the world will see a historic change".
We don't know the details of that document yet.