Newsround's Guide to North Korea
For decades North Korea - also known as the Democratic People's Republic of 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.
What is life like in North Korea?
The people of North Korea live under a form of communist rule. They don't have a say in how their country is run.
The government strictly controls all aspects of daily life. Most people are forbidden from travelling outside the country.
All TVs and radios are tuned to state channels and looking at foreign television is against the law.
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 donations from the United Nations for food.
Who's in charge?
Korea was formally split into two separate countries, North and South Korea, on 9 September, 1948.
The governments of both countries didn't agree on many things and don't get on to this day.
Since 1948, North Korea has been ruled by three men from the same family.
Kim Il-sung was in charge until his death in 1994, when he passed on the Presidency to his son Kim Jong-il.
Kim Jong-il died in 2011, and North Korea announced his son, Kim Jong-un as its new leader.
Around a million people gathered in the capital city, Pyongyang, to hear the announcement.
A report by the US Committee for Human Rights suggests that there are up to 200,000 people in prison and labour camps in the country, because they have disagreed with the government.
Why are people worried about North Korea?
It's thought that North Korea has been developing big weapons for decades.
The country has more than 1,000 missiles, including long-range missiles which it is feared could one day be used to strike other countries like America and Japan.
Many think the country is also working on making nuclear weapons, powerful bombs that can cause a lot of damage.
North Korea is one of the most heavily militarised countries in the world. Its one million strong army is considered to be the fifth largest in the world.