On Sunday, North Korea launched a ballistic missile 1,311 miles into the air, exiting the Earth’s atmosphere and flying five times higher than the International Space Station, according to the autocratic state’s internal media agency. While it’s difficult to verify the North Koreans’ numbers, the first test of the Hwasong-12 missile, a “newly-developed ballistic rocket capable of carrying a large-size heavy nuclear warhead,” appears to be an “unqualified” success that experts say could put the country on track to developing a functional Intercontinental Ballistic Missile, or ICBM.

The North Korean state media agency announced the successful test on Monday. The rocket landed about 489 miles from its launch point in the ocean off North Korea’s northeastern coast, according to U.S. and other international officials watching the launch.

If the missile were fired on a more traditional launch trajectory, analysts predict it could have a range of up to 2,800 miles — not long enough to reach Hawaii or the U.S. mainland, but definitely enough to hit Guam, the closest major U.S. territory to North Korea.

“An Unqualified Success”

“This is an unqualified success,” Melissa Hanham, a Senior Research Associate in the East Asia Nonproliferation Program (EANP) at the Center for Nonproliferation Studies told Inverse. “It’s not maybe a success, it’s not sorta a success, they took that thing, they launched it very far, and they definitely proved they have Guam in range.”

The North Koreans have now conducted 10 missile tests in 2017 alone, but the most recent launch is one of the most significant in years. Here’s why you should be paying attention, and what to look for next from North Korea’s ballistic missile program.

Understanding the Missile’s Weird Flight Plan

Unlike many missile tests, North Korea launched the missile almost straight up into the air, blasting it in a high parabolic arc that easily exited the Earth’s atmosphere. Hanham says that NK picked this flight plan for two specific reasons. The first reason is relatively obvious: North Korea doesn’t really have anywhere to shoot a missile without pissing someone else off. Other countries, like Russia, China, and the United States can blast ICBMs and shorter-range missiles over vast empty stretches of their own territory or the ocean and not cause an international incident, but North Korea’s precarious location in the middle of China, Japan, South Korea, and Russia means that where ever it aims, someone’s going to get nervous (NK state media acknowledges this, saying that “the test-fire was conducted at the highest angle in consideration of the security of neighboring countries.”)

Warhead barbecue. Rodong Sinmun

The second reason is more interesting. North Korea has been testing the re-entry system for a long-range ballistic missile since at least 2016 (ICBMs leave the Earth’s atmosphere, so must have shielding like a spacecraft to make sure the warhead doesn’t just burn up coming back into the atmosphere). The first test, Hanham says, essentially just “flame broiled” a mock warhead with the engine of a SCUD missile, but the most recent launch shows that North Koreans potentially have a viable system capable of re-entry. It’s important to note, however, that the North Korean government are the only ones who know whether or not the heat shield on the Hwasong worked or not.

“It’s all sorta been leading up to this moment.”

Over the past year, and especially the past few months, Hanham says North Korea has been putting the pieces together for a working ICBM. The heat shield test is one example, but the regime has also been experimenting with different fuel sources and testing missiles in various sizes and designs. Thae Yong-Ho, a former North Korean ambassador who defected to South Korea in August 2016 told NBC News that Korean rule Kim Jong Un is desperate to develop a working ICBM that makes him a threat on the world stage: even if North Korea has nukes, it can’t flex its might without a way to use them.

“It’s all sorta been leading up to this moment,” Hanham says. “This is essentially the weapon with the farthest range they’ve ever tested. So yeah, it’s bad news.”

The Center for Nonproliferation Studies has an interactive database and map of every North Korean missile test and launch since 1984.

So what’s next?

Hanham and other experts say that the Hwasong-12 could be the building block for a future ICBM. U.S. officials have been careful to state that on its own, the Hwasong-12 is an intermediate range ballistic missile and not an ICBM — yet. There are a couple ways that it could become one.

Analysts think the Hwasong-12 uses the new, high-thrust engine North Korea tested in March.

One way of making an ICBM platform would be to “cluster” several of the new engines, increasing the overall power of the rocket. The other way is to make a “staged” missile, similar to the systems that launch many spacecraft and satellites into orbit, where a lower stage propels a rocket up, then an upper stage rocket kicks in, dropping the lower stage and continuing the missile’s flight. A clustered engine test or a new staged rocket test would be a major benchmark in progress toward an ICBM.

What happens if North Korea tests an ICBM?

This is where things get, well, bad. President Donald Trump called North Korea a “flagrant menace” after the latest test, and would be faced with an unprecedented threat from the nation if it succeeded in testing an ICBM. A two-stage ICBM launch is a major achievement, and because of North Korea’s aforementioned geographic location, even the test flight could be enough to put the world on the brink.

“Once they get to that point it’s going to be really dicey diplomatically around the world,” Hanham says. “It’s going to be very difficult for people to tell when it’s a test and when it’s the start of a war.”