What is an ICBM and why should we be worried because North Korea has one?

What is an ICBM?

An intercontinental ballistic missile (ICBM) is a missile that has the ability to carry a warhead more than 3,400 miles either through the air, or through space.

The missile must be able to survive re-entry if it flies through space.

The missile would normally be used to deliver a nuclear weapon  but could carry conventional warheads.

An ICBM is different from other ballistic missiles because it can be launched more quickly and can fly farther than other ballistic missiles.

What does “ballistic missile” mean?

A ballistic missile is powered and guided toward a target but falls under gravity onto its target. The trajectory is a high, arching path.

What kinds of missiles has North Korea tested?

Pentagon officials said they detected an ICBM launched on July 28 by North Korea.

It traveled about 620 miles from Mupyong-ni, where it was launched, before splashing down in the Sea of Japan. The trip took about 45 minutes.

>> Related: North Korea fires intercontinental ballistic missile, Pentagon says

North Korea previously said it launched a Hwasong-14 missile on July 4.

According to U.S. officials, it was a two-stage missile that they had never seen.

The missile flew as high as 1,741 miles before it hit a target off the coast of Japan some 580 miles away from its launch site. It took 39 minutes to hit the target.

Despite claims from North Korea that the missile could hit any target in the world, analysts say the Hwasong-14 likely has a range of 4,970 miles. Alaska is 3,560 miles from North Korea.

Can the missile deliver a nuclear weapon to the U.S. mainland now?

Weapons experts believe that the North Koreans are likely about two years away from developing a missile that can reach the United States mainland. The U.S. is 6,434 miles from the Korean Peninsula.

There has been no evidence that North Korea has miniaturized a nuclear warhead, something they would have to do to deliver such a weapon to the U.S. mainland.

Can the U.S. shoot it down?

The job of the Missile Defense Agency is to develop ways to defend against such weapons. However, a test of a new defense system carried out in Japan in June did not have great results. The test of the SM-3 intercepter failed.

A defense system that North Korean officials often refer claim is threatening to its people is the THAAD (Thermal High Altitude Area Defense) system. THAAD is meant to intercept short-, medium- and intermediate-range missiles. It has a range of around 125 miles.

Why be concerned?

North Korea's leader is considered unstable and his regime is a brutal one. It is believed that North Korea spends between one-quarter and one-third of its GDP on the military and weapons development in a country where nearly 2 million people starved to death in the 1990s.

On the first of the year, Kim promised that his country would carry out a test of an ICBM. After seven months, it has. Defense officials in North Korea say they exploded a hydrogen bomb in 2016.

Kim has vowed to use the weapons the country is now testing. On Wednesday, he said North Korea would "demonstrate its mettle to the U.S." and that its weapons programs would never be part of any negotiation with the United States.