As North Korea saber-rattles and the Trump administration talks tough, it’s a good time to remember some history lessons from the first Korean War that are still applicable today.

The Trump administration’s increasingly tough talk on North Korea and the apparent defiance from the young North Korean dictator have made many people wonder if a second Korean War is imminent. At this critical junction, it’s probably best to remind ourselves of some history lessons from the first Korean War, which are still applicable today.

1. Don’t Forget Russia

Today many people seem to count only China, the United States, and North and South Korea as the major players on the Korean Peninsula. Let’s not forget the important role the former Soviet Union (today’s Russia) historically played, which contributed to the conflict on the Korea Peninsula today.

After Japan surrendered to the Allies on August 15, 1945, the Soviet army took over Manchuria and quickly marched into Korea. Joseph Stalin was keen to control Korea for at least three strategic reasons: it would expand communism’s sphere of influence; give the Soviet Union access to a Pacific warm-water port; and prevent the Korean Peninsula from becoming a launching pad for military actions against the Soviet East Asia territory.

The United States pushed back against the Soviet advance by creating an agreement that chose the 38th parallel as a separation line, thus constraining Soviet influence to north of the 38th parallel, while limiting the U.S. influence to south of the 38th parallel. That’s how we are left with two Koreas today.

The Soviets selected a communist, Kim II-Sung (grandfather of Kim Jong-Un), to be the new leader of North Korea in 1946, which ushered in the next seven decades of the Kim’s family’s dictatorship of North Korea. The Soviet Union provided military advisors to North Korea and equipped Kim’s army with Soviet weapons. A Chinese scholar, Shen Zhihua, has documented in great detail based on declassified former Soviet archives the Soviet Union’s massive military aid to North Korea.

It’s Stalin who gave Kim II-Sung final permission to invade South Korea in 1950. Shen’s analysis shows Stalin was initially against Kim’s invasion plan out of concern that the United States might intervene. What changed Stalin’s mind, according to Shen, were two U.S. events.

First, President Harry Truman announced on January 5, 1950 that the United States would not challenge the claim that Taiwan was part of China. Second, Secretary of State Dean Acheson excluded Taiwan and South Korea from America’s defense perimeter in the western Pacific. Stalin probably believed these public announcements indicated the United States was retreating from East Asia.

Therefore, during Kim’s secret trip to Moscow in April 1950, Stalin gave Kim II-Sung his final blessing for an invasion of South Korea (a bonus lesson: authoritarian regimes are always emboldened by perceived U.S. retreat). Interestingly, it was also Stalin who insisted on Kim securing China’s active involvement as a condition for his blessing.

There’s no question of the Soviets’ outsized role in shaping the events in Korea decades ago. After the Soviet Union dissolved in 1989, the relationship between Russia and North Korea was strained after Russia formally recognized South Korea in 1990. However, Russian President Vladimir Putin sought to renew that old alliance by paying North Korea a historic visit in 2000. Kim Jong Il, father of King Jong-Un, visited Russia several times in return.

It’s safe to assume that Moscow won’t stand idly by if the United States takes on North Korea through any military action. Just like China, Moscow has very vocally objected to the United States installing a missile defense system in South Korea. To protect Russia’s strategic interests in Korea, Putin could wade into the Korean Peninsula like he did in Syria.

2. Don’t Be Arrogant

One of the most important lessons from the First Korean War is that sometimes arrogance is our worst enemy. In his new book, “The Beautiful Country and The Middle Kingdom,” John Pomfret wrote that China had warned the United States not to cross the 38th parallel. Since China and the United States hadn’t established a formal diplomatic relationship at that time, China chose India’s ambassador to China, K. M. Panikkar, to let the United States know that if U.S. troops invaded North Korea, China would be forced to intervene.

China’s repeated warnings met arrogance. Pomfret wrote “the CIA suggested that the Chinese were bluffing. Secretary of State Dean Acheson called (China’s) warnings ‘mere vaporings of a panicky Panikkar.’” Some U.S. military leaders were equally arrogant. General Douglas MacArthur “simply closed his ears to the growing presence of Chinese troops in Korea.” His intelligence chief, Major General Charles Willoughby, had no respect for Chinese soldiers. “Willoughby thought no ‘Chinaman’ would dare to take on the mechanized might of the US armored cavalry,” Pomfret writes.

The CIA, U.S. military leaders, and some politicians were so blinded by arrogance that they failed to anticipate Mao’s recklessness and fell short of understanding China’s bottom line. Mao had been preparing the Chinese army to go to Korea since the summer of 1950. He wanted to participate in this war because it provided him an opportunity to achieve multiple goals: challenge a superpower, establish his own international prestige, and consolidate power domestically.

More importantly, China needed North Korea to be a buffer against any possible land invasion. When United Nations troops, most of whom were Americans, reached the Yalu River (a natural border between China and North Korea) on November 21, 1950, it breached China’s bottom line. The rude awakening for the United States came on November 25, 1950, the day the U.S. Army was caught off-guard when China sent 300,000 troops across the Yalu River to help North Korea fight the UN troops.

Compared to the UN troops, the Chinese troops were poorly fed and equipped, but they had one advantage: a seemingly unlimited supply of manpower. Mao was willing to achieve his goals at any human cost. During the two-year period of Chinese involvement in the Korean War, it’s estimated that China committed 3 million troops, and approximately 400,000 to 1 million Chinese soldiers were killed. But it’s the first war China fought and hadn’t lost since 1840. So for Mao, the Korean War was a success because he not only gained international prestige but became more popular and powerful domestically.

From Eisenhower to Obama, every U.S. president criticized their predecessors’ dealings with China and proclaimed they would do better. Yet none succeeded once in office. With the growing tension on the Korea Peninsula, Trump should not overestimate his own deal-making power and believe somehow he can convince China to “solve” the North Korea problem for him. China and North Korea have drifted away over the years, but China’s bottom line hasn’t changed: North Korea remains a buffer zone for China.

3. Don’t Forget Soft Power

Winning a war is not just about military means and hardware. Soft power is a concept developed by Joseph Nye of Harvard University to describe the ability to shape others’ preferences and attitudes through non-coercive (non-military) means.

‘Hating America became one of the key pillars of the Communist revolution and remains one of its most nettlesome legacies today.’

In 1950, the Chinese public was told that South Korea, with the United States’ support, had started the Korean War by invading North Korea. Even today, Chinese school books continue to make this claim to Chinese children. While Chinese soldiers were fighting in North Korea in the 1950s, Mao launched a nationwide campaign against the United States. “Hating America became one of the key pillars of the Communist revolution and remains one of its most nettlesome legacies today,” Pomfret says.

Since the United States and China normalized their diplomatic relationship in 1979, the United States has done surprisingly little to push back on China’s false claims. In the meantime, the history of the Korean War is largely forgotten here in America. Many Americans today probably know very little of it, so they naturally ask why the Trump administration is focusing on North Korea now and why Americans should care about what’s happening on the Korean Peninsula?

It’s important that the Trump administration address these questions so it can build public support for any possible future actions. In the meantime, Trump should take whatever history lesson President Xi gave him with a grain of salt, and urge Xi to present the historical truth of the Korean War to Chinese people.

Today, South Korea and North Korea are real-life symbols of freedom versus subjugation. Robert Farley wrote, “the Korean War was anything but accidental, but miscalculation and miscommunication both extended and broadened the war beyond its necessary boundaries.” There are many lessons policy makers today should learn from it before they start talking about the next war.