There has been a big argument between the United States of America and North Korea.
It's happened many times before because the government in Pyongyang, the capital of North Korea, has been testing Nuclear weapons.
Reports in the US say North Korea has now made nuclear missiles small enough to reach America.
If you want to know more about North Korea take a look at our guide.
What is a nuclear missile?
A nuclear missile is a powerful bomb.
Bombs like this can affect people and the environment for years after the bomb has been dropped.
What is being done about this?
Countries have been angry with North Korea for a long time because of their nuclear testing.
And this is just another part of an ongoing argument between America and North Korea.
This is partly because America has for a long time supported South Korea.
Donald Trump is the latest US president to send warships and submarines to South Korea.
He is trying to get North Korean leader Kim Jong-un to stop his weapon-building plans.
The United Nations has even got involved. They are a group of countries who come together to make rules so that everyone can live in peace.
They have asked North Korea to stop building weapons .
After the new reports of smaller missiles, American President Donald Trump has warned North Korea to stop threatening the US.