Historians have always debated the questions, "What caused the great dynasties of the world to fall?" and more specifically, "What brought down the Tang, Yuan, and Ming Dynasties in China?"
Sometimes, the causes seem to be obvious: a neighboring kingdom invades and conquers the state, a king dies without leaving an heir, or the military turns upon the ruler and ousts him. Recently, however, evidence from the natural world shows that there may be underlying environmental reasons for the decline and fall of empires.
Evidence from Wangxiang Cave, China
A joint Chinese and American team of researchers examined a 118 mm (4.65 inch) section of a stalagmite from the Wangxiang Cave in Gansu Province, China. Chemical analysis of the stalagmite revealed the relative strength of the monsoon rains over a period of 1,810 years.
Stalagmites form from the slow dripping of rainwater through limestone caves. Scientists can determine how rainy the weather was in a particular year by looking at the isotopes, or different types, of oxygen that were deposited in the stone that makes up a stalagmite.
The rock's age is revealed by uranium and thorium dating, allowing chemists to compare their scientific record with the historical record of China's dynastic cycle. What they found is quite amazing.
The "Mandate of Heaven" is Shown in Rainfall
Chinese philosophers since the Zhou Dynasty (1122–256 B.C.) have theorized that emperors receive the "Mandate of Heaven," or support from the gods, if they rule wisely and justly. When an emperor becomes a tyrant, the Mandate is revoked and the dynasty falls.
This theory kept emperors from wielding unlimited power, and provided a handy rationalization for any army general or nobleman who sought to overthrow the emperor and establish a new dynasty of his own.
Now, it seems, scientific evidence indicates that the Mandate of Heaven literally fell from the sky - in the form of rainfall.
Cycles of Dryness
The stalagmite reveals that the monsoon rains fell off substantially between about 860 and 930 A.D. Another decades-long dry spell hit between 1340 and 1380 A.D., and a third from 1580 to 1640 A.D.
Monsoon rains that had moved north from the Indian Ocean no longer made it to much of central and northern China, and the land grew parched. This spelled big trouble for the emperors.
Political Effects of the DrynessFall of the Tang Dynasty
The Tang Dynasty was established in 618 A.D. It is still considered to be one of the pinnacles of Chinese civilization, a sort of golden age.
Throughout the ninth century, however, the dynasty began to lose its grip. Tang power was dealt a death-blow in the year 873 A.D., when a horrific drought and famine swept China. Agricultural production, already decreased in recent years by the lack of rain, fell by more than half. People and livestock starved.
Clearly, the Tang Dynasty was losing the Mandate of Heaven.
The following year, the decade-long Huang Chao Rebellion began. Huang Chao was an illegal salt-trader, one of a multitude driven into criminal activity by the drought and famine. He organized the starving people of his region into a remarkably successful guerrilla army. In 880, Huang Chao's army even captured the capital city of Chang'an (now called "Xi'an").
Huang Chao seized the throne, but he ruled from Chang'an for just one year before being driven out by Emperor Xizong's forces. Huang Chao committed suicide in 884, and the rebellion ended, but not before the Tang Dynasty had been terribly weakened by this uprising of the starving peasantry.
In 907, with the weakness of the monsoon rains still in force, the last Tang emperor Ai was deposed by an army general. China plunged into the Five Dynasties and Ten Kingdoms Period, a time of chaos and violent political fragmentation that lasted until the establishment of the Song Dynasty in 960.
It is worth noting that a particularly strong monsoon rain peak also began in 960, and lasted until 1020.The Fall of the Yuan Dynasty
The culprit? You guessed it. According to the evidence from Wanxiang Cave, the monsoons failed.
As with the rulers of the late Tang Dynasty, the late Yuan emperors were beset by drought, famine, rampant crime, and civil unrest.
The ethnic-Han Chinese rose up in 1351 in the "Red Turban Rebellion," which was put down by the Yuan Army only after three years of bitter fighting.
Meanwhile, another rebel named Zhu Yuanzhang led his peasant army against the Yuan, capturing Jainkang (Nanjing) in 1356. His power grew as the rains stayed away. In 1368, Zhu Yuanzhang defeated the Yuan emperor Toghun Temur, and founded the Ming Dynasty.
By 1380, monsoon rainfall had spiked impressively.The Fall of the Ming Dynasty
The new Ming rulers of China had a much longer run than their predecessors, the Yuan, but in the end, they were laid low by the same force that did in the Mongols.
Trouble began for the Ming during the reign of the Wanli Emperor, who ruled from 1572 to 1620 (a span that includes much of the driest period). China was beset by the same cold, dry weather that afflicted Europe; this was known as the "Little Ice Age."