What are some of the costliest mistakes ever made in history?

When the Jin dynasty underestimated the Mongol Horde.

The painful thing about this, is that the Jin didn’t just underestimate the Mongols once, but several times. These mistakes resulted in one of the deadliest series of conquests in history.

In the 12th century the Mongols were a group of nomads living on the edge of civilization in northern Asia. They were expert horsemen, and had perfected the art of firing a bow while riding, which made them dangerous on the battlefield.

The Mongols had submitted to Chinese rule for centuries, and were constantly at war with other nomadic tribes in the region. Many of these wars were instigated by the Chinese as a means to keep the tribes divided.

Then Genghis Khan came to power, and united the various nomadic tribes of Northern Asia.

As Genghis Khan grew more powerful, and more tribes joined his cause, the Jin watched on. The Jin dynasty was one of the most powerful nations in East Asia. They had hundreds of thousands of soldiers at their disposal, one of the largest populations in the world, and some of the most advanced technology.

Despite their advantage, the Jin completely missed the ball when Genghis Khan rose to power. When the tribes were still divided the Jin could have easily defeated them, but instead they actually allied with Genghis Khan to defeat a mutual enemy, the Tatars.

As Genghis Khan expanded his power he began to raid the borders of the Western Xia dynasty, a state in central China.

(You can see the Jin in blue, and the Western Xia in Green)

These raids eventually turned into a full scale Mongol invasion of the Western Xia. The Emperor of the Western Xia repeatedly requested support from Jin, but the Jin dynasty refused to send assistance. They wanted to watch their two enemies, the Xia and Mongols, destroy each other, and didn’t consider the Mongols a great enough threat to get involved.

This was another fatal mistake, the combined armies of the Western Xia and Jin could have potentially defeated the Mongols and saved the lives of millions of people, but the Jin were too consumed in their own self interest to send assistance.

The Mongols surrounded the Western Xia capital of Yinchuan and forced them to surrender. A major factor in the decision to surrender was that no help was coming from Jin. Had the Jin sent help, the Western Xia could have potentially continued the war.

By now the Mongols controlled most of North Asia, including the Western Xia who became a vassal of the Mongol horde.

At this point the Jin could have begun preparations for war, but didn’t respect the Mongol threat enough. They could have drafted hundreds of thousands of soldiers, but instead wasted precious time tending to their own matters.

In 1211 the Mongols launched an invasion of the Jin dynasty. The Jin army that was sent to meet them was much smaller, undertrained, and horribly led. It was a mere fraction of the several hundred thousand troops the Jin could have had, if they respected the Mongol threat enough and had adequately prepared.

The Jin leadership balked at the ensuing Battle of Yehuling and missed an opportunity to attack the Mongols first in terrain that was ill suited for the Mongol horsemen. Instead they sent diplomats to try and negotiate peace, wasting time, and allowing the Mongols to formulate a plan to defeat them. The army was crushed and the Jin missed an opportunity to defeat the Mongols before they could further establish themselves in the region.

The Jin held off the Mongols for decades, a testament to how powerful the Jin actually were, but eventually they collapsed and were absorbed into the Mongol Empire.

In the end, the Jin dynasty made several disastrous mistakes. From failing to attack the Mongols first, to refusing to aid the Western Xia, to allowing Genghis Khan to become so powerful. The root cause of many of their mistakes though was overconfidence. They underestimated the power of the horde, and overestimated their own ability to defeat it.

The result of their indecision, overconfidence, and repeated mistakes was one of the deadliest military conflicts ever.

During the century after the invasion of Jin, the Mongols launched military campaigns across Eurasia that led to the deaths of as many as 40 million people. Some scholars argue that Mongol expansion also contributed to the spread of the Black Plague which killed an additional 200 million+ people. Regardless of whether the plague is connected or not, the Mongols killed a lot of people.

We are basically looking at one of the deadliest series of conquests in history, surpassed only by World War II, and possibly the Taiping Rebellion.

The cost of these wars was horrific. Tens of millions of lives lost, cities across Eurasia sacked, and entire regions depopulated for centuries to come. All this devastation came about because the Jin dynasty made the mistake of underestimating the power of the Mongols.