After decades of rising tension on the Korean Peninsula, relations with North Korea have reached a fever pitch in the first 100 days of the Trump Administration. Repeated missile tests and military parades to celebrate national holidays are not uncommon in the Democratic People’s Republic of Korea (DPRK). The U.S. response, however, has changed significantly from years past.

At its core, U.S. posture toward the DPRK looks consistent with past administrations: a combination of economic and financial sanctions, defense support for regional U.S. allies such as South Korea and Japan, and an attempt to persuade China to apply political and economic pressure to change North Korean behavior, with the ultimate goal of getting to the negotiating table to find a diplomatic solution rather than regime change or a preemptive strike.

What is different under the Trump Administration is a matter of degree. The administration has ratcheted up the rhetoric on every prong of the North Korea strategy. Declaring an end to the policy of “strategic patience,” the Trump Administration talks openly about a kinetic military option in North Korea and has deployed an aircraft carrier and strike group to the waters off the Korean Peninsula.

All of this raises questions about why North Korean missile tests threaten the United States. The DPRK is estimated to maintain an arsenal of more than 1,000 missiles of varying ranges. A missile is only a delivery mechanism; the payload could be anything from a satellite to a weapon—or a nuclear warhead.

There are four main aspects of the North Korean threat to America, outlined below.

1) Regional Allies

First, the proximity of strong American allies to North Korea puts U.S. interests at stake. The United States has long-standing defense treaties with both South Korea and Japan. These treaties stipulate that an attack on either country would present a danger to the United States—and they require the U.S. action in defense of South Korea or Japan, if attacked. America’s global leadership is largely based on its system of alliances, and meeting mutual defense treaty obligations is at the core of this system. Early in his administration, President Trump has recognized this reality and dialed back some of his comments as a candidate, emphasizing the importance of U.S. commitments to countries like South Korea and Japan in Asia as well as the NATO alliance in Europe.

2) U.S. Military

Second, the presence of U.S. military bases, assets, and troops in Northeast Asia puts American lives and matériel at direct risk. The mutual defense treaties with South Korea and Japan also establish provisions to station American military forces in those countries. Currently, South Korea and Japan host over 75,000 U.S. troops. North Korea’s short-range missiles have the capability to reach up to 300 miles, giving the DPRK the ability to strike any part of South Korea’s territory, including any of the U.S. military bases there. With a range of over 600 miles, North Korea’s medium-range missiles are capable of reaching Japan. North Korea announced that a recent round missile launches were specifically intended as practice for striking U.S. bases in Japan.

3) U.S. Homeland

Third, as North Korea’s ballistic missile capability increases, there is the potential that the country could launch a missile able to reach the U.S. homeland. An intercontinental ballistic missile (ICBM) would give North Korea the capability to strike targets thousands of miles away. The West Coast of the United States is just over 5,000 miles away from North Korea. While the DPRK has never tested an ICBM, the country has three times in recent years tested multi-stage ballistic missiles with an estimated range of between 3,000 and 9,000 miles. All three tests failed. However, North Korea has twice successfully launch satellites into orbit with a rocket technology similar to an ICBM. Many experts believe these rocket launches are ballistic missile tests in disguise.

4) Nuclear Program

Finally, the North Korean missile program clearly threatens U.S. interests with the prospect of a nuclear payload. The DPRK has conducted five nuclear tests since 2006. The pace of these tests appears to be increasing, with two tests in 2016 alone. North Korea’s most recent nuclear test was the biggest one yet, with a yield initially reported to be 10 kilotons and later estimates ranging from 20 to 30 kilotons. (The bomb that the United States dropped on Hiroshima during World War II yielded 15 kilotons.) The real threat is the combination of North Korea’s nuclear program and its missile capability. DPRK officials claim to have developed the capability to mount a nuclear warhead on a ballistic missile, and the South Korean government has assessed this to be true.

Fundamentally, a bellicose North Korea threatens peace, stability, and security in the Asia-Pacific region. With its repeated missile launches and nuclear tests, North Korea represents a serious threat to the U.S. interests, including regional allies, deployed troops, and even the homeland.