China built a big, beautiful wall, too. It failed.

From the moment he launched his campaign for president, Donald Trump compared the barrier he wanted to build along the U.S. southern border to China’s Great Wall. With the U.S. government now shuttered by the standoff over funding Trump’s wall, both he and his Democratic opponents might want to take a closer look at the Chinese fortification – and why exactly it failed.

The Great Wall visited by tourists today is the handiwork of the Ming Dynasty (1368-1644) and was primarily constructed in the mid-to-late 16th century. The common perception is that the wall was conceived as a single, massive infrastructure project to protect China’s tumultuous northern border from foreign invaders. It was nothing of the sort. The Great Wall was built to a great degree by default, by a political system too paralyzed by infighting to come up with anything better.

Border security had been a preoccupation of China’s imperial court from its earliest days. “Barbarians” from the northern steppe – whether Xiongnu, Turk, Jurchen, Mongol or other – routinely threatened the Middle Kingdom. Some, such as Genghis Khan’s Mongols in the 13th century, managed to overrun the entire empire.

The long northern boundary ran through inhospitable terrain that made it difficult to defend. Chinese emperors had tried a variety of methods to secure the border, from buying off the barbarians to mounting massive military expeditions against them. The problem would always return when a new batch of tribesmen appeared across the frontier.

The Ming Dynasty compounded the usual difficulties of securing the border with a combination of arrogance, division and indecision. The Ming court was an especially raucous place where hostile factions were almost constantly at each other’s throats. The border issue often got dragged into these contests for palace power.

Generally, the Ming, having reclaimed the empire from Genghis Khan’s descendants, leaned toward a tough line against their northern neighbors, often denying them the opportunity to trade with China. The Mongols were dependent on such trade for the grain and other supplies they needed to survive on the inhospitable steppe. So they were left little choice but to launch raids into China to plunder what they needed. The attacks both hardened opinion in China against the Mongol tribes and heightened the urgency for more border security.

The fractured Ming court groped for a solution. Some officials advocated a more diplomatic approach that would restore trade and alleviate the pressure on the Mongols to raid. They were usually shouted down by more hawkish mandarins who thought such policies smacked of appeasement. The latter argued that Mongol requests for trade relations were just a ploy by the untrustworthy barbarians to lull the Chinese into a vulnerable complacency.

These hawks often favored military action to push the raiders away from the border. But, sending troops into the northern wastes to chase nomadic horsemen was costly, difficult to organize and widely unpopular. Proposals often got entangled in the arcane, personal intrigues between palace notables jockeying for imperial favor.

That seemed to leave the court with one option: building defensive barriers to keep the barbarians out. “Unwilling to trade with the Mongols, and unable to defeat them militarily, by the middle of the sixteenth century the Ming had no policy choice left but to attempt to exclude the nomads by building walls,” historian Arthur Waldron wrote in his exhaustive study “The Great Wall of China: From History to Myth.”

The strategy proved effective in blunting Mongol raids – where walls were built. The problem was that the mobile horsemen could easily shift their assaults to undefended areas of the border. That’s exactly what a large Mongol force did in 1550 when it penetrated to the Beijing suburbs. The response of the court was to build more walls. The Great Wall was the result of this haphazard defense policy.

The tragedy is that the Ming’s big, beautiful wall failed to fulfill its sole mission: to protect China from invasion. The Ming were still tinkering with the massive structure when the dynasty collapsed in 1644. Amid the resulting chaos, a new steppe power, the Manchus, descended from the north, snatched Beijing and ruled as the Qing Dynasty.

Maybe the Manchu conquest was beyond repulse. A China divided was bound to fall. But, the Ming clearly contributed to their own catastrophe. A court environment that prioritizing defeating one’s internal rivals over cooperating on policy stymied any hope of developing an effective solution to a serious problem. Emperors, coddled in luxurious palaces and lacking any real knowledge of conditions along the border, preferred looking tough on foreigners to compromise. Resistance to mutually beneficial trade deepened the causes of instability along the border. Treating those others across the frontier as bandits to be thwarted rather than poor people in need doomed Ming policy to failure.

Sound familiar? The ultimate lesson of the Great Wall of China is that a physical barrier, no matter how expensive and impressive, will fail if detached from a broader set of policies to alleviate the sources of insecurity along the border. The Ming never figured that out. Hopefully Washington’s mandarins will.

Michael Schuman, who is based in Beijing, is the author of “The Miracle: The Epic Story of Asia’s Quest for Wealth” and “Confucius and the World He Created.”