North Korean leader Kim Jong Un. KCNA via Reuters When North Korea fired a missile over Japan on Tuesday, it violated the island nation's sovereign territory and defied the United Nations. And if Japan doesn't do anything about it, experts say Pyongyang will most likely walk all over it.

North Korea has reached a point with its long-range missile tests where it needs to fire them on normal trajectories, which means flying over Japan.

In previous tests, North Korean intercontinental ballistic missiles have flown almost straight up in the air and landed only a few hundred miles away, though they're meant to travel thousands of miles.

Now North Korea needs to find out how to guide the warheads when they're flying at something.

"There is a technical imperative for conducting this test," Mike Elleman, an expert on missiles at the International Institute for Strategic Studies, told The Washington Post. "They want to be able to look at reentry dynamics and how it performs on a more normal trajectory."

Given North Korea's need for these kinds of tests over Japan, if Japan doesn't respond strongly enough, it can only expect the tests to continue.

"In a way, it's kind of a trial balloon," Elleman said. "If we overfly Japan, what happens? If the blowback isn't too significant, they will feel more comfortable with launching a Hwasong-14 to a good distance to validate its performance on a normal trajectory."

Tal Inbar, the head of the space research center at the Fisher Institute for Air and Space Strategic Studies, tweeted after the launch: "NK missile flight over Japan is an Archimedean point for the US. No REAL ACTION — and we will see more missiles on the same path soon."