SEOUL — North Korea has test-fired a flurry of missiles in recent weeks, culminating Tuesday with the launch of an intermediate-range ballistic missile over Japan into the Pacific Ocean. The test missile, which traveled farther than any previous rocket launched by the country, was the latest demonstration of the North’s growing and increasingly sophisticated military arsenal.

The escalation comes as its leader, Kim Jong-un, has sought to solidify the country’s stance as a nuclear-armed power and his position at its helm. Last month, North Korea adopted a new law saying it would launch a nuclear strike “automatically and immediately” if the command and control system for its nuclear forces — an apparent reference to Mr. Kim’s leadership — was put in danger.

As the risk of nuclear war grows once again with Russia’s invasion of Ukraine, Mr. Kim earlier this year pledged to expand the North’s nuclear arsenal “at the fastest possible speed.” He said that it was not merely a deterrent but could be used “if any forces try to violate the fundamental interests of our state.”

North Korea has carried out 23 weapons tests so far this year, involving a total of 43 ballistic and cruise missiles. It conducted four tests just last week, in apparent protest of joint military exercises between the U.S., South Korea and Japan.

President Biden has warned of “responses” if North Korea continues to escalate tensions on the Korean Peninsula, but his calls for additional United Nations sanctions earlier this year were blocked by Russia and China. The international community and the United States have repeatedly tried both sanctions and dialogue to persuade North Korea to ​give up its ​nuclear ​weapons programs. Neither has worked.

Mr. Kim, the North Korean leader, said last month there would “no longer be any bargaining over our nuclear power.”

While it’s difficult to get a clear, up-to-date picture of North Korea’s military capabilities, analysts and observers agree that in the decade under Mr. Kim’s rule, North Korea​ has rapidly expanded its nuclear program and modernized its missile fleet. The expansion of the arsenal is a growing threat to the United States and its allies​ in the region. ​Here’s what’s in it.

North Korea’s ballistic missiles can carry nuclear warheads, and the country conducted six increasingly sophisticated underground nuclear tests between 2006 and 2017. The last four of them happened under Mr. Kim.

This year, Washington and Seoul have repeatedly warned that North Korea is gearing up for another nuclear test at Punggye-ri, where the North conducted all of its previous underground nuclear tests.

Its last and most powerful nuclear test was conducted in September 2017, when North Korea claimed to have detonated ​a thermonuclear​, or hydrogen, bomb. ​Estimates of the device’s explosive power ranged from 50 to 300 kilotons.

A mere 100 kilotons would make the test six times as powerful as the bomb dropped on Hiroshima in 1945.​

North Korea has extracted plutonium, an atomic bomb fuel, from its Soviet-designed nuclear reactor in Yongbyon, north of Pyongyang. It also runs centrifuges to produce weapons-grade enriched uranium, another bomb fuel.

As of 2021, North Korea had enough fissile material for 40 to 50 nuclear warheads and could produce enough for six or seven bombs a year, according to an estimate by the Arms Control Association. The United Nations’ nuclear watchdog last year said that North Korea may be preparing to ramp up its production of plutonium and highly enriched uranium in Yongbyon.

North Korea demonstrated the biggest strides in its weapons capabilities in 2017.

That year, the country fired its intermediate-range ballistic missile, Hwasong-12, over Japan and threatened an “enveloping” strike around the American territory of Guam. It also test-fired Hwasong-14 and Hwasong-15, the country’s first intercontinental ballistic missiles.

By the end of the year, Mr. Kim claimed that his country had the ability to launch a nuclear strike against the continental United States.

After 2017, Mr. Kim stopped testing nuclear weapons and long-range missiles but threatened to end his moratorium when talks with President Trump collapsed in 2019.

During a nighttime military parade in the fall of 2020, North Korea displayed a new, untested I.C.B.M. that looked bigger than any of the previous ones.

In March, North Korea appeared to conduct its most powerful I.C.B.M. test to date. While state media called it the larger Hwasong-17, showcasing the missile in a Hollywood-style propaganda video, South Korea later said it appeared to be the older Hwasong-15. The South said that clips and photos of the launch were faked to exaggerate Mr. Kim’s weapons achievements for a domestic audience.

The biggest unanswered question is whether North Korea has mastered the technology needed to send an intercontinental nuclear warhead into space and then guide it back through the earth’s atmosphere to its target. North Korea has yet to demonstrate that its warhead can survive the intense heat and friction created by re-entry.

When North Korea resumed missile tests in 2019 following the collapse of the Kim-Trump talks, the tests featured three new weapons, code-named KN-23, KN-24 and KN-25 by outside experts.

They each marked big advances in North Korea’s short-range ballistic missile program.

Unlike its older missiles that used liquid fuel, all three of the new missiles used solid fuel. The new solid-fuel weapons, mounted on mobile launchers, are easier to transport and hide and take less time to prepare. And at least two of them, KN-23 and KN-24, could perform low-altitude maneuvers, making them harder to intercept.

At a military parade in 2021, North Korea displayed what looked like a bigger, upgraded version of KN-23. Photos released by the North Korean media indicate that it was the newly developed tactical guided missile North Korea launched in March ​of that year.

The new missile was developed to be larger than KN-23 in order to carry a bigger warhead and more fuel. North Korea claimed that the missile could carry a 2.5-ton warhead. South Korea’s defense minister later admitted that his military missed part of the North Korean missile’s trajectory because of its midair maneuvering.

North Korea also test-launched “long-range cruise missiles” in September 2021. It called them a “strategic weapon,” indicating that it would arm the new missile with nuclear warheads. Also in 2021, North Korea began testing what it called a ballistic missile with a detachable “hypersonic” gliding warhead.

The country’s missile tests have demonstrated that they were becoming harder to intercept.

It has also been testing submarine-launched ballistic missiles since 2015.

During military parades in 2020 and 2021, North Korea displayed what looked like two upgraded versions of its Pukguksong submarine-launched ballistic missiles. It currently has only one submarine that can launch a ballistic missile but says it is building a new one with greater capabilities.

North Korea has one of the largest standing armies in the world, with more than one million soldiers. But much of its equipment is old and obsolete, and the military lacks fuel and spare parts.

It has sought to make up for its shortcomings by building nuclear weapons, which it says are primarily a deterrent.

In a speech before the Supreme People’s Assembly in September, Mr. Kim said the North would not give up its nuclear weapons as long as nuclear weapons and “imperialism” exist on the Earth. He said: “We have drawn the line of no retreat regarding our nuclear weapons so that there will be no longer any bargaining over them.”

“Pyongyang has been in a dizzying sprint to build an arsenal that contains the kinds of advanced capabilities you would find in the United States or Russia,” said Adam Mount, senior fellow at the Federation of American Scientists. “But for the most part, these have been single-serving demonstrations: Pyongyang tests the system once then moves onto the next one. It’s less clear whether they will complete testing or deployment of any or all of these systems.”