Today, South Korea is a robust democracy with a thriving, high-tech economy. Its products—think Samsung phones and Hyundai cars—are exported all over the world, as are its music, TV shows, and movies.

North Korea, on the other hand, is a repressive Communist dictatorship in which millions face hunger and the government executes political opponents. It has also built up a nuclear weapons program that threatens South Korea and the roughly 28,000 American troops stationed there.

Continually on the brink of conflict, the Korean peninsula presents President Donald Trump with one of his key foreign policy challenges.

South Korea is a thriving democracy.  It has a high-tech economy that exports products all around the world. Samsung phones and Hyundai cars are made there. South Korean music, TV shows, and movies are everywhere.

North Korea, on the other hand, is a repressive Communist dictatorship. Millions of people face hunger, and the government executes political opponents. It threatens South Korea with a nuclear weapons program. The roughly 28,000 American troops stationed in South Korea also face this threat.

Always on the edge of conflict, the Korean peninsula presents President Donald Trump with one of his key foreign policy challenges.

So how did we get here? The tensions on the Korean peninsula date back to a war that began 75 years ago. On June 25, 1950, North Korea launched a brazen attack against its southern neighbor. With the help of United Nations (U.N.) ground forces led by the U.S., the fighting ended in 1953. But in many ways, the conflict has never been resolved.

“The Korean War is the forgotten war, sandwiched between World War II and the Vietnam War, so many Americans don’t remember it,” says Jim Walsh, a Korea expert at the Massachusetts Institute of Technology. “The characters and the conflicts we see in the Korean War are still playing out today, and that makes it an important war in ways we didn’t appreciate at the time.”

So how did we get here? On June 25,  1950, North Korea launched a bold attack against its southern neighbor. The fighting ended in 1953 with the help of United Nations (U.N.) ground forces led by the U.S. But in many ways, the conflict has never been resolved.

“The Korean War is the forgotten war, sandwiched between World War II and the Vietnam War, so many Americans don’t remember it,” says Jim Walsh, a Korea expert at the Massachusetts Institute of Technology. “The characters and the conflicts we see in the Korean War are still playing out today, and that makes it an important war in ways we didn’t appreciate at the time.”

The roots of the conflict can be traced to World War II (1939-45). Japan had long occupied Korea, brutally repressing its people and even forbidding them from using their language. During the war, the U.S., the United Kingdom, and France allied with the Soviet Union against Japan and the other Axis Powers, Germany and Italy. When Japan surrendered in 1945, the Americans and Soviets agreed to temporarily occupy Korea to oversee the withdrawal of Japanese forces. They divided the peninsula at the 38th line of latitude, or the 38th parallel.

Soviet dictator Joseph Stalin, whose country controlled the northern half, and President Harry S. Truman initially agreed that the two halves would unite and Koreans would choose their future leaders in elections. But the Cold War—the long contest for global influence that pitted the U.S. and its democratic allies against Communist nations led by the Soviet Union—was deepening. Stalin soon refused to participate in the Korean elections.

In 1948, a U.S.-backed government became the Republic of Korea—better known as South Korea. The Soviet-backed North then declared itself the Democratic People’s Republic of Korea, what most of the world calls North Korea. Despite the “Democratic” in its name, it was headed by a Communist named Kim ll Sung, a former major in the Soviet army and the grandfather of North Korea’s current leader, Kim Jong Un. He quickly gained dictatorial powers.

The beginning of the conflict can be traced to World War II (1939-45). Japan had long occupied Korea. It brutally repressed the Korean people and even banned the use of their language. During the war, the U.S., the United Kingdom, and France allied with the Soviet Union against Japan and the other Axis Powers, Germany and Italy. In 1945 Japan surrendered. At that time, the Americans and Soviets agreed to temporarily occupy Korea to oversee the withdrawal of Japanese forces. They divided the peninsula at the 38th line of latitude, or the 38th parallel. The Soviets controlled the northern half and the Americans the southern.

Soviet dictator Joseph Stalin and President Harry S. Truman initially agreed that the two halves would unite.  Koreans would choose their future leaders by holding elections. But the Cold War was intensifying. The U.S. and its democratic allies were fighting against Communist nations led by the Soviet Union for global influence.  Stalin soon refused to participate in the Korean elections.

In 1948, the U.S.-backed government became the Republic of Korea. It is better known as South Korea. The Soviet-backed North then declared itself the Democratic People’s Republic of Korea, what most of the world calls North Korea. Despite the “Democratic” in its name, it was headed by a Communist named Kim ll Sung. He was a former major in the Soviet army and the grandfather of North Korea’s current leader, Kim Jong Un. He quickly gained dictatorial powers.

Then in 1949, Communists under Mao Zedong won a civil war in China and seized control of the Chinese government. The West feared that Communism was spreading. So in June 1950, when North Korea attacked the South and occupied South Korea’s capital, Seoul, Truman believed he had to take a stand. He turned for help to the United Nations, which authorized its member states to fight the invaders. (Though 16 countries would eventually send troops, most were South Koreans and Americans.)

Early on, the U.N. forces, led by General Douglas MacArthur of the U.S., seemed poised for victory. After retaking Seoul in September 1950, they began making their way across the 38th parallel and toward North Korea’s border with China. But in October of that year, Mao sent some 300,000 Chinese troops to aid North Korea. Outnumbered, the U.N. forces soon retreated back to the 38th parallel.

With the war at a stalemate, peace talks opened in July 1951. It took two years of negotiations for representatives from the U.S., North Korea, and China to finally sign an armistice, leaving the North-South border close to where it had been at the start of the war. The agreement created a 2.5-mile-wide demilitarized zone (D.M.Z.) along the border that would serve as a buffer between the two nations.

But the peace was incomplete. South Korea was unwilling to accept anything less than a unified Korea and refused to sign the armistice. To this day, no formal peace treaty has ever been signed. The war—which left an estimated 5 million dead, including nearly 37,000 American soldiers—has technically never ended.

Neither North Korea nor South Korea had achieved its goal: the destruction of the opposing regime. The devastation, however, was widespread, especially in the North, where most of the fighting took place and where the U.S. bombed extensively. Historians say as many as 70 percent of the dead may have been civilians.

Today the D.M.Z. remains one of the most heavily secured borders in the world. Tens of thousands of North Korean and South Korean troops stand guard against attack by the other country. The U.S. has also kept tens of thousands of troops in South Korea since the end of the war to prevent an attack from the North.

Then in 1949, Communists under Mao Zedong won a civil war in China. When Communists took control of the Chinese government, the West feared the spread of Communism. So in June 1950, when North Korea attacked the South and occupied South Korea’s capital, Seoul, Truman believed he had to take a stand. He turned for help to the United Nations.  While 16 countries would eventually send troops, most were South Koreans and Americans.

Early on, the U.N. forces, led by General Douglas MacArthur of the U.S., seemed poised for victory. They retook Seoul in September 1950. Then they began making their way across the 38th parallel and toward North Korea’s border with China. But in October of that year, Mao sent some 300,000 Chinese troops to aid North Korea. Outnumbered, the U.N. forces soon retreated back to the 38th parallel.

With the war at a stalemate, peace talks started in July 1951. It took two years of negotiations for representatives from the U.S., North Korea, and China to finally sign an armistice. It left the North-South border close to where it had been at the start of the war. The agreement also created a 2.5-mile-wide demilitarized zone (D.M.Z.) along the border. It would serve as a buffer between the two nations.

But the peace was incomplete. South Korea was unwilling to accept anything less than a unified Korea and refused to sign the armistice. No formal peace treaty has ever been signed. The war—which left an estimated 5 million dead, including nearly 37,000 American soldiers—has technically never ended.

Neither North Korea nor South Korea has achieved its goal of destroying the other country’s government. The destruction, however, was widespread.  Most of the fighting took place in North Korea where the U.S. bombed extensively. Historians say as many as 70 percent of the dead may have been civilians.

Today the D.M.Z. remains one of the most heavily secured borders in the world. Tens of thousands of North Korean and South Korean troops stand guard against attack by the other country. The U.S. has also kept tens of thousands of troops in South Korea since the end of the war to prevent an attack from the North.

In the years since the war, South Korea has risen from being one of the world’s poorest countries into its 14th largest economy. “K-culture” has swept the globe, and the nation’s internet connections are among the fastest in the world. Though the nation faced unrest in December after President Yoon Suk Yeol briefly imposed martial law and was later impeached, South Korea has had a stable democratic government for nearly four decades.

North Korea, on the other hand, is an authoritarian state where anyone who challenges the country’s leaders faces arrest, imprisonment in one of the regime’s labor camps, or death by firing squad. Most North Koreans don’t have access to the internet, and the government controls all media outlets.

“North Korea and South Korea have gone in such different directions—the differences couldn’t be more extreme,” says Jean Lee, a Korea expert at the East-West Center, a Hawaii-based think tank.

Since 2006, North Korea has been under strict international sanctions as punishment for its nuclear weapons program. In recent years, the regime has turned to a state-sponsored cyber-theft program—using hackers to steal from banks and cryptocurrency companies—as a way to get around sanctions and fund its nuclear program, Lee says, adding that those attacks have generated hundreds of millions of dollars for the regime.

The state spies intensively on its own citizens to ward off any challenges to the Kim regime. Kim has invested in making the North Korean capital, Pyongyang, a showcase city, but the rest of the country has few paved roads, little to no electricity, and often no running water or heat.

“The 3 million people who live in Pyongyang are the elite, and everyone else is very poor,” Lee says. “The city is closed and manned by guards. You cannot get into the capital, much less live there, without permission.”

In the years since the war, South Korea has risen from being one of the world’s poorest countries into its 14th largest economy. “K-culture” has swept the globe. The nation has some of the fastest internet connections in the world. South Korea has had a stable democratic government for nearly four decades. The nation faced unrest in December after President Yoon Suk Yeol briefly imposed martial law, but he was later impeached.

North Korea, on the other hand, is an authoritarian state. Anyone who challenges the country’s leaders faces arrest, imprisonment in labor camps, or death by firing squad. Most North Koreans don’t have access to the internet. The government controls all media outlets.

“North Korea and South Korea have gone in such different directions—the differences couldn’t be more extreme,” says Jean Lee, a Korea expert at the East-West Center, a Hawaii-based think tank.

Since 2006, North Korea has been under strict international sanctions as punishment for its nuclear weapons program. In recent years, the regime has turned to a state-sponsored cyber-theft program. It uses hackers to steal from banks and cryptocurrency companies. It is a way to get around sanctions and fund its nuclear program, Lee says, adding that those attacks have generated hundreds of millions of dollars for the regime.

The government spies intensively on its own citizens to ward off any challenges to the Kim regime. Kim has invested in making the North Korean capital, Pyongyang, a showcase city. However, the rest of the country has few paved roads, little to no electricity, and often no running water or heat.

“The 3 million people who live in Pyongyang are the elite, and everyone else is very poor,” Lee says. “The city is closed and manned by guards. You cannot get into the capital, much less live there, without permission.”

U.S. officials have long considered North Korea to be one of America’s gravest threats, despite its poverty and isolation. It has one of the world’s largest militaries, with 1.3 million soldiers. And despite the efforts of the international community, it has developed a stockpile of nuclear warheads, as well as missiles capable of striking the U.S. mainland, according to Bruce Klingner, a Korea expert at the Heritage Foundation, a Washington, D.C., think tank.

North Korea also has a sophisticated cyber warfare operation that’s capable of launching attacks on other countries’ infrastructure and transportation, Klingner adds.

For decades, the two Koreas have swung between periods of conciliation and saber-rattling. Relations have sunk to new lows in the past few years, as North Korea has ended talks with South Korea and the U.S. and has increasingly viewed South Korea as its enemy.

During President Trump’s first term, he met with Kim Jong Un three times and praised the dictator. He scaled down joint military exercises between the U.S. and South Korea, and he has said he thinks South Korea should pay more for U.S. military protection. With Trump in office, many South Koreans wonder how much they will be able to rely on the U.S. alliance to protect them from the North.

Last year, North Korea and Russia signed a mutual defense treaty, deepening longstanding ties between the two autocratic nations. Russia has been increasingly isolated from the international community since its 2022 invasion of Ukraine, so a partnership with North Korea—another international pariah—makes sense.

Since they signed the treaty, North Korea has been sending large quantities of weapons to Russia to replenish its diminishing stockpile. In November, North Korea sent at least 10,000 troops to fight for Russia in the war against Ukraine. In return, Russia has sent oil and missiles to North Korea.

These developments have only added to the rising tensions on the Korean peninsula.

“The Korean War seems very long ago, like ancient history,” says Klingner. “But the threat is still there. In fact, the North Korean threat has only grown.”

U.S. officials have long considered North Korea to be one of America’s most dangerous threats, despite its poverty and isolation. It has one of the world’s largest militaries, with 1.3 million soldiers. Despite the efforts of the international community, North Korea has a stockpile of nuclear warheads. This includes missiles that can strike the U.S. mainland, according to Bruce Klingner, a Korea expert at the Heritage Foundation, a Washington, D.C., think tank.

North Korea also has a sophisticated cyber warfare operation that’s capable of launching attacks on other countries’ infrastructure and transportation, Klingner adds.

For decades, the two Koreas have swung between periods of relative calm and saber-rattling. Relations have sunk to new lows in the past few years. North Korea has increasingly seen South Korea as its enemy. Peace talks with South Korea and the U.S. have ended.

During President Trump’s first term, he met with Kim Jong Un three times and praised the dictator. He scaled down joint military exercises between the U.S. and South Korea. He has said he thinks South Korea should pay more for U.S. military protection. With Trump in office, many South Koreans wonder how much they will be able to rely on the U.S. alliance to protect them from the North.

Last year, North Korea and Russia signed a mutual defense treaty, deepening longstanding ties between the two autocratic nations. Russia has been increasingly isolated from the international community since its 2022 invasion of Ukraine. A partnership with North Korea—another international outsider—makes sense.

Since they signed the treaty, North Korea has been sending large quantities of weapons to Russia to replace its diminishing stockpile. In November, North Korea sent at least 10,000 troops to fight for Russia in the war against Ukraine. In return, Russia has sent oil and missiles to North Korea.

These developments have only added to the rising tensions on the Korean peninsula.

“The Korean War seems very long ago, like ancient history,” says Klingner. “But the threat is still there. In fact, the North Korean threat has only grown.”