7 Questions About North Korea’s Nuclear Missiles You Were Afraid to Ask

North Korea on Tuesday fired a ballistic missile that flew over Japan’s northern island Hokkaido and landed in the Pacific Ocean, leading U.S. President Donald Trump to say that “all options” are under consideration when it comes to dealing with the rogue state.

This is the thirteenth missile launch from North Korea since January and the fourth since North Korea threatened to strike U.S. territory in the Pacific Ocean on August 9., one day after President Donald Trump said he would react with “fire and fury” should Pyongyang continue its threatening behavior.

Early in August the United Nations Security Council approved a new $1 billion sanctions package against North Korea. The move was response to the country’s ongoing nuclear and missile development efforts. U.S. intelligence officials have reportedly determined that North Korea has developed a nuclear warhead small enough to fit inside its long-range missiles, a major escalation of the country’s capabilities.

If you haven’t been following the North Korea crisis closely, you might have some basic questions about it you’re afraid to ask. Here are some answers:

Why has North Korea targeted Japan?

The U.S. and South Korea currently have 67,500 troops engaged in joint military exercises on the Korean peninsular. Japan’s own military is currently limited to self-defense due to a clause in their 1947 constitution stating that Japan will not maintain “land, sea, or air forces or other war potential” after the Second World War.

This isn’t the first time that North Korea has launched a missile at Japan. Twice before, in 1998 and 2009, the state said it was launching a satellite when it flew rockets out towards the Pacific Ocean. But this particular launch is likely to renew calls within Japan to host anti-missile technology – THAAD or Aegis Ashore anti-missile batteries – that China would be opposed to.

“In some ways it is devilishly well-calibrated,” Prof. Stephan Haggard, a Korea expert at the UC San Diego School of Global Policy and Strategy, told TIME, speaking about Tuesday’s launch. “It’s driving a wedge between Seoul, Washington and Beijing on this issue.”

Why do the U.S. and North Korea not get along?

The U.S. and North Korea’s poor relationship stems back to the mid-20th century. After the Second World War, the U.S. took control of what became South Korea, while the Soviet Union oversaw the communist North. The two were temporarily established as separate countries in 1948, but in 1950 Pyongyang, backed by China, invaded the south in an attempt to reunify the peninsula, kicking off the Korean War. The U.S. led a U.N. effort to support South Korea in the bloody battle, which ended three years later. The war devastated the North, which, despite having around half of the South’s population, suffered the vast majority of the conflict’s casualties.

After the war, North Korea became a hermit state under Supreme Leader Kim Il Sung. Over the years, its totalitarian leaders — Kim Il Sung’s son Kim Jong Il, and subsequently his grandson Kim Jong Un — have repeatedly blamed the U.S. for its problems, particularly its economic sanctions and isolation. In return, America is wary of North Korea developing nuclear and ballistic weapons and launching an attack on U.S. soil, as it has threatened to do a number of times.

What is North Korea capable of doing?

The U.S. Defense Intelligence Agency (DIA) has concluded that North Korea now has nuclear weapons small enough to fit inside its missiles, The Washington Post reports. Pyongyang launched its missile development program in 1976, and last month successfully tested two missiles that appear capable of reaching U.S. territory.

ICBMs, or Intercontinental Ballistic Missiles, are capable of carrying nuclear warheads over 3,000 miles through the air. However, intelligence agencies did not previously believe that North Korea had the capability to deliver a nuclear warhead using such a missile, as it’s difficult to make the weapons small enough to be effective. “The United States has not seen North Korea demonstrate a capability to miniaturize a warhead,” Pentagon spokesman Peter Cook said last year.

A North Korea missile test last month only flew about 580 miles, but it reached an altitude of over 1,700 miles. David Wright, co-director of the UCS Global Security System, said that means the missile has the potential to travel over 4,000 miles. “That range would not be enough to reach the lower 48 states or the large islands of Hawaii,” he wrote. “But would allow it to reach all of Alaska.”

After the test, arms control specialist Jeffrey Lewis tweeted: “That’s it. It’s an ICBM. An ICBM that can hit Anchorage [Alaska] not San Francisco, but still.”

North Korea is equipped with missiles that can travel shorter distances as well. In September 2016 it fired three missiles that each flew about 600 miles before landing in the sea. In February 2017 it fired an intermediate-range missile that flew about 300 miles, before also falling into the sea. These tests are evidence that Pyongyang can threaten nearby U.S. allies, like South Korea and Japan.

Is Kim still threatening Guam?

Kim seems to have backed down on his threat to surround the U.S. territory of Guam by a “ring of fire,” saying he would merely watch the “foolish and stupid” U.S. before making a decision. Yet some experts suggest that Tuesday’s launch might have been designed to show the small island that it can follow through with its threats.

Guam it has been a strategic outpost for the U.S. military since the end of World War II, with over 6,000 troops currently stationed at Air Force and Navy bases there. Guam has a total population of over 160,000 people.

Those bases are also key to the U.S. military’s strategy in dealing with North Korea. Amid the ongoing tensions, several American bombers have taken off from Guam to fly so-called “show of force” flights over the Korean peninsula.

Because Guam is only about 2,000 miles from North Korea, experts believe it’s within range of Pyongyang’s missiles. The U.S. has a missile defense system known as THAAD located on the island.

Madeleine Bordallo, Guam’s delegate to the U.S. House of Representatives, said that the Pentagon has assured her the territory is well protected. But she told CNN that she is concerned about the situation and takes North Korea’s threats “very seriously.”

What has the U.S. done to stop North Korea?

The U.S. has periodically pursued diplomatic solutions to North Korea’s isolation, but to no avail. Previous administrations have tried “freezes” of North Korea’s nuclear-weapons programs in exchange for diplomatic inducements, although any successes were only temporary — such as a 2007 agreement by North Korea to shutter nuclear facilities that collapsed within two years.

In addition, the U.S. has heavily sanctioned North Korea’s economy since 2008, when then-President George W. Bush issued an executive order labeling North Korea a national threat. In February 2016, President Obama tightened sanctions on the rogue state, a month after North Korea conducted a fourth test of a nuclear weapon. The latest U.N. sanctions appear to be a continuation of that strategy.

President Donald Trump has signaled a more aggressive approach than his immediate predecessor, confronting Pyongyang and urging China to pressure North Korea to halt its nuclear ambitions. Earlier this year, Vice President Mike Pence warned that the “era of strategic patience” with North Korea was over. Trump on Tuesday warned he would meet threats with “fire and fury.”

Why doesn’t the U.S. just bomb North Korea’s nuclear facilities?

Because it doesn’t want to start a war. Any pre-emptive strike by the U.S. would have deadly consequences for its allies that neighbor North Korea. South Korea and Japan are well within North Korea’s striking distance; indeed, the city of Seoul is just 35 miles from the de-militarized zone between the two countries. There is no way to know for sure that any attack would completely destroy Kim’s collection of weapons, some of which are hidden in hillside bunkers.

“Military action just isn’t feasible — that’s the bottom line,” John Delury, an East Asia expert at South Korea’s Yonsei University, previously told TIME. “It just doesn’t pass any cost-benefit analysis.”

Why does President Trump want China to resolve the North Korea issue?

Trump has put pressure on China to confront its neighbor and ally over recent missile launches that violated U.N. resolutions, believing only the Asian nation — with its vast economic leverage over North Korea — has the power to tame Kim Jong Un’s aggressive behavior.

China has reduced exports of coal to North Korea in response to missile tests, but as Trump pointed out in a tweet on Wednesday morning, trade between the two has continued to surge. In the first three months of 2017, China-North Korea trade rose by 37.4% over the same period the year before.

In April, the U.S. President tweeted that “if [China] want to solve the North Korean problem, they will,” but he later backtracked after a meeting with China’s President Xi Jinping. “[I] realized it’s not so easy,” Trump told the Wall Street Journal following the meeting. “I felt pretty strongly that they had a tremendous power [over North Korea]… But it’s not what you would think.”

Trump said in the same WSJ interview that he offered Xi better trade terms with the U.S. in exchange for China’s cooperation in taming North Korea. “I explained to the President of China that a trade deal with the U.S. will be far better for them if they solve the North Korean problem,” he explained on Twitter. President Xi did not offer Trump any public commitments on North Korea in return.