Much of North Korea -- and its armed forces -- has been a mystery to the world since it was formed in 1948. But it's not all secret. Because of the country's penchant for holding military parades and firing test missiles, we've been able to gather a lot of information about the increasingly aggressive nation and its capacity for war.
Here's what we know about North Korea, its military, and its worrisome nuclear program.
There are plenty of heavy machines in the North Korean military. According to a Newsweek analysis, North Korea has 3,500 tanks, 72 submarines, 302 helicopters, 563 combat aircraft and 21,100 pieces of artillery.
North Korea has been making headlines lately thanks to its aggressive ballistic missile tests.
This picture taken on May 14 and released from North Korea's official Korean Central News Agency (KCNA) shows the country's leader Kim Jong-Un (third from the right) inspecting a ground-to-ground medium long-range strategic ballistic rocket, called Hwasong-12, at an undisclosed location.
On July 4, 2017, North Korea conducted a test launch of its new Hwasong-14 intercontinental ballistic missile, seen here in a photo released to news agencies. It flew for approximately 40 minutes before landing in the Sea of Japan.
Though North Korea claims its new weapon can strike "anywhere in the world," the United States Department of Defense says the missile has a theoretical range of roughly 3,400 miles -- barely enough to reach the western coast of Alaska.
This picture, dated May 14, 2017 by North Korea's state news agency, shows the launch of a Hwasong-12 missile. Officials in South Korea and Japan say the test missile, which landed roughly 60 miles south of Russia, flew 430 miles and reached an altitude of 1,245 miles, Reuters reports.
Less than a week later, North Korea tested a second missile, the Pukguksong-2, a ground-to-ground, medium-to-long range strategic ballistic missile. The May 21 test flew just 310 miles before crashing into the Sea of Japan, the New York Times reports.
Here, a group of North Koreans watch the test on a big screen in central Pyongyang.
It's not just North Korea's missiles that have Asia worried -- the country has been more aggressive in its nuclear testing as of late, too. In January 2016, North Korea tested what it claimed to be a hydrogen bomb at its underground Punggye-ri test site. That was followed by another 20- to 30-kiloton test blast in September.
Secretary Tillerson has said that further nuclear testing by North Korea would result in economic sanctions from China, the country's main trading partner, according to the Washington Times.
Caption byFox Van Allen
/ Photo by NurPhoto, NurPhoto/Getty Images
Though North Korea claims its "mid-to-long-range" missiles can carry a nuclear warhead, military analysts suggest it is not a real threat -- yet -- to the US, or its strategic military bases in Guam in the Western Pacific.
"Based upon the analysis of related authorities," South Korean military spokesman Col. Roh Jae-cheon told the New York Times, "the missile cannot reach" Guam.
North Korea's missiles may merely be an expensive show of strength. Here, a Hwasong-type missile is rolled through the streets of Pyongyang during an April military parade.
Amnesty International estimates that North Korea is spending up to 22 percent of its gross domestic product on its military. (North Korea state media puts the figure at 15.8 percent.) At the same time, an estimated 40 percent of North Korea's population suffers from malnourishment, according to the UN.
Missiles aside, one of North Korea's most formidable assets may be the sheer size of its military. Because the country has universal conscription, North Korea's military has 1.19 million active members and another 7.7 million in reserve.
Here, the Korean People's Army marches through Kim Il-Sung square in Pyongyang on April 15, 2017.
The tanks and troop transports seen in parades such as these represent a motorized world far beyond the reach of most North Koreans. Only military and government officials are allowed to own motor vehicles in the country.
This particular military parade, held on April 16, celebrated the 105th anniversary of the birth of North Korean leader Kim Il-Sung.
The first supreme leader of North Korea, Kim Il-Sung is viewed by many in North Korea as having a divine provenance. He ruled from the country's creation in 1948 until his death in 1994. His son Kim Jong-Il ruled until 2011. Today, North Korea is ruled by Il-Sung's grandson, Kim Jong-Un (seen here waving).
Though the Korean War ended with the signing of an armistice on July 27, 1953, there was no formal peace treaty between the two sides. As such, tensions between North Korea and US-fortified South Korea have remained high for decades.
Today, the two countries are divided by a 160-mile-long, 2.5-mile-wide strip of land known as the Korean Demilitarized Zone (DMZ) that is free of heavy weaponry. The Associated Press reports that North Korea keeps an estimated 60 percent of its forces adjacent to the line.
South Korea has discovered four tunnels under the DMZ -- apparent attempts by North Korea to create an invasion route. The first tunnel, discovered in 1974, had already been fortified with concrete, wired with electricity and equipped with a narrow railway capable of transferring 20,000 soldiers per hour.
Today, these "tunnels of aggression" are guarded by the South Korean military and are available for visit by tourists.
Though the US has little to fear from North Korean missile attacks, the South Korean capitol of Seoul is just 35 miles from the DMZ. As such, the US has pledged to assist its allies in the South by granting it access to a powerful missile defense system.
Here, South Korean farmer In-Suk Hwang stands next to the DMZ fence on the island of Gyodong.
In March 2017, the US military began rolling out the Terminal High Altitude Area Defense (THAAD) system to South Korea. It is designed to protect the country against the short- and medium-range missiles in the North's arsenal.
Here, trucks unload the THAAD at Osan Air Base in Pyeongtaek, South Korea.
The THAAD missile defense system does not use explosive warheads, instead relying on kinetic energy to destroy incoming missiles. That is, its guided missiles just smash into their targets instead of detonating. It was developed, in part, as a defense against the Scud missiles launched by Iraq during the Gulf War in 1991.
The highly successful system was first deployed by the US military in 2008.
THAAD isn't without controversy. Both Russia and China have major concerns over the system, as it would reduce the effectiveness of their own weapons in the region.
Here, residents of Seongju county participate in a protest against the recently installed THAAD system nearby, on March 18. The locals object to the radiation emitted by THAAD's system's powerful radar, VOA News reports.
Though the explosive fire power of North Korea's weapons registers well on camera here, few believe the country could actually win a war against South Korea or the US. Still, the North could inflict massive amounts of damage in a relatively short time.
"It's just, how much damage can [Kim Jong-Un] do before we take him out?" retired Air Force Gen. Herbert Carlisle told Military Times.
There are more than 25 million people in the Seoul metro area alone. Any war between the North and South would likely start a humanitarian crisis. And should North Korean troops press into the South Korean capital, America's ability to provide air cover would be limited.
Making the possibility of war even more grim, it's estimated that North Korea possesses anywhere between 2,500 and 5,000 tons of chemical weapons it could launch against the South.
North Korea's unconventional methods of warfare would likely extend to the internet, as well. The UN is investigating a May 8 cyberattack against its 1718 Committee, which investigates violations of the economic sanctions currently levied against North Korea.
The hackers allegedly had "very detailed insight" into the committee and its investigations, Reuters reports. North Korea is also suspected to be behind the WannaCry ransomware attack earlier in the month.