"This is clearly directed at Japan," said Carl Schuster, a professor at Hawaii Pacific University and former director of operations at the US Pacific Command's Joint Intelligence Center.
"For the last month or so they've been very careful not to do things that could be provocative in South Korea," former US Ambassador Christopher Hill told CNN. "The usual betting is when North Korea provokes in this kind of way, the harder line, the right-of-center, tends to benefit in (South) Korea."
Abe called the test "absolutely intolerable," while Japanese Chief Cabinet Secretary Yoshihide Suga said it was "a clear provocation to Japan and the region."
South Korean officials say analysis suggests the missile is a modified intermediate-range ballistic missile (IRBM), a Musudan-level missile.
It flew 500 kilometers (310 miles) before crashing in the Sea of Japan, also known as the East Sea, sources said.
IRBMs typically have a range of 3,000 to 5,500 kilometers (1,864 to 3,417 miles) -- much farther than needed to hit South Korea, but not long enough to hit the lower 48 states (though Guam is in its range.)
Abductions and conquerors
Japan and North Korea do not have active diplomatic relations, but there has been progress to normalize them in recent years.
One of the big holdups has been the cases of Japanese citizens who were abducted by North Korea
in the 1970s and 1980s.
Pyongyang has admitted and apologized for the incidents, but it's yet to provide an explanation that was acceptable to the Japanese -- who say that diplomatic relations can't be normalized until the abduction issue is resolved.
North Korea's hostility toward Japan stems from its close relations to South Korea -- which Japan calls
its "most important neighbor" -- and the United States.
But North Korea demonizes Japan domestically, using World War II-era characterizations focusing on the occupation of the Korean peninsula, according to Schuster.
Just a show?
There's two aspects to every North Korean military test: the technical and the political.
Even if a test is called a failure, there's a lot the North Koreans -- and its adversaries
-- can learn.
"There are a lot of things that those who fire missiles are testing whenever they do these kinds of things," says retired US Lt. General Mark Hertling.
"They're trying to get distance, they're trying to read things like does the missile fall apart. They may have been testing some type of heat shield on the reentry vehicle. They may have been testing whether the missile could withstand G's (gravity forces) given a payload."
The political aspect is both domestic and international.
At home, it's a way for Kim to prove to his base that he's a strong leader making progress on his promises. Abroad, they serve as provocative messages to Pyongyang's adversaries, reminding foes about North Korea's military capabilities. And they're usually timed to hammer the message home and maximize media coverage.
"They do things as much for political reasons as they do for military reasons," Schuster says. "The launch is more significant politically than operationally -- it's the first shot since Trump took office, it comes just 10 days after (current secretary of defense and retired) Gen. Mattis promised the Japanese and the South Koreans against the North Korean nuclear threat."
If it was an IRBM, the launch distance means it was likely a failure technically -- but not geopolitically, according to Schuster.
"It's very likely that the IRBM they wanted to launch wasn't ready, so they shot what they had. Political intent is the same, operational test probably didn't meet their expectations," he said.
The missile that really keeps US defense officials up at night is the intercontinental ballistic missile (ICBM), which -- if working properly -- could deliver a nuclear payload to the United States.
US and South Korean officials told CNN
in January that North Korea might be readying two ICBMs for a test launch in the near future.
Though Kim says his country is in the "final stages" of readying the missile for a test launch, many analysts believe it's a ways away -- Schuster said he believes it will be another five years before they get one.
The THAAD question
Preparing for a potential ICBM attack -- and hopefully being able to shoot it down -- is a key pillar of US defense policy with regard to North Korea.
And every launch by Pyongyang is an impetus for Japan and South Korea to improve missile defense systems.
"The South Korean government will secure the lives of citizens and the national security from North Korea's threat based on a strong joint defense system between the South Korea and the US" Cho June-Hyuck, a spokesman for the South Korean Foreign Ministry, said after the Sunday missile launch.
He's likely referring to the Terminal High Altitude Area Defense system (THAAD).
THAAD is designed to detect an ICBM and take it down before it can hit a target.
South Korea announced in July that it planned to deploy the system in Seongju County, about 155 miles (250 kilometers) southeast of Seoul.
"When the North Koreans provoke, more and more Koreans say we need that system," Hill said. "We (the US) need to get those fielded. We need to do whatever we can to support our allies, South Korea and Japan. We need to really step up that kind of cooperation."
THAAD isn't deployed in Japan, but there have been reports that Tokyo is considering it.
That would draw the ire of China and Russia, who are both vehemently opposed to the missile system.
Both countries believe that the US is playing up the defensive nature of the missile system and using its deployment to geopolitically box them in
-- if it can stop North Korea's missiles, couldn't it stop China's and Russia's too?
"Americans only talk about it in a tactical sense, it's a useful tool alongside a bunch of others to deter North Korea or stop a missile mid-flight," says Professor John Delury of Yonsei University. "The Chinese look at THAAD in strategic terms, and what they see is THAAD as part of a bigger picture of a missile defense network along its perimeter."