Sorry, I realized last night that the scale of the teaser for Part II I posted was simply too massive, so I had no choice but to split it.
This second part will focus on the following questions:
- Why has China historically often been divided into a northern and southern dynasty?
- Why were southern dynasties always on the defensive?
- Why were northern expeditions either unsuccessful or extremely difficult?
- The necessity of "defending the Yangtze must begin with defending the Huai [River]."
- A speculative scenario of a modern-day divided China resembling the Southern and Northern Dynasties period.
Let’s first address the first question: the
geographical reasons behind the division into a northern and southern dynasty. Although all East Asian regions experienced periods of north-south division, China's Northern and Southern Dynasties period stands out as the most classic and extensive example. On such a grand scale, the impacts arising from geographical factors were more pronounced than in other regions. Upon closer examination, we can actually identify common geographical underpinnings behind the distribution patterns of north-south divisions across East Asia.
As with yesterday, let’s examine the following three maps:
- A (relatively simplistic) depiction of China’s four major climatic zones.
- The distribution of arid farmland versus paddy fields.
- A map showing the January 0°C isotherm.
Compared to the maps I shared yesterday, we can still observe another striking similarity. There exists a hidden boundary between northern and southern China—one determined by climate and geography—that has shaped the country's division into north and south. This boundary is geographically known as the
Qinling-Huaihe Line, marking the dividing zone between temperate monsoon climate and subtropical monsoon climate.
This climatic demarcation indirectly influenced the agricultural-pastoral frontier further north, which in turn played a role in shaping the broader geopolitical dynamics of East Asia.
We also know that monsoon climates are inherently unstable, being primarily driven by temperature fluctuations. Higher temperatures intensify the summer monsoon, causing the rain belt to shift northward. This northward movement of the rain belt results in increased humidity in the north, gradually transitioning the region toward a subtropical monsoon climate.
Rice, as a staple crop, yields significantly higher harvests than traditional northern crops like millet and broomcorn millet, and far more than wheat. Although rice was not considered a strategic grain reserve during the Tang Dynasty due to insufficient preservation techniques, the abundant rice harvests of that era were still sufficient to propel the dynasty into a period of prosperity and trigger a population explosion.
Moreover, the subtropical monsoon climate brings additional changes. For instance, vegetation on the Loess Plateau increases, sediment levels in the Yellow River decrease, and the likelihood of catastrophic flooding diminishes. Compared to the temperate monsoon climate, the subtropical variant is more stable, with significantly fewer droughts. All these factors strengthen the power of an agrarian empire. Of course, increased precipitation also enhances the strength of nomadic populations.But, we have some less favorable news.
This climatic shift also causes the agricultural-pastoral boundary to move northward, allowing agrarian empires to achieve unprecedented levels of strength. This enables the transformation of previously unsuitable lands into arable farmland.
And here’s another sobering reality: while the
3,000-meter-high Qinling Mountains effectively block the
Southwest Monsoon from penetrating deep into the north, the
Huai River, which primarily flows through plains, fails to stop the
Southeast Monsoon. The Southeast Monsoon struggles even more to reach the lands west of the
Loess Plateau, meaning the
Hexi Corridor’s oasis grasslands and the northern
Gobi Desert receive little additional rainfall or expanded pastureland.
Thus, while nomads do gain some marginal benefits, they remain vastly outmatched by a
Central Plains dynasty that is twice—or even four times—their strength.
Reviewing Chinese history, we observe that the most powerful dynasties capable of defeating northern nomadic empires and expanding northward all emerged during periods of
higher average temperatures, while weaker dynasties coincided with
colder climates. Notably, the game’s key periods—the
Yuan, Ming, and Qing Dynasties—all occurred under
relatively cool conditions.
The
Yuan and
Qing Dynasties managed to control the grasslands through mechanisms distinct from traditional Han-majority dynasties (we’ll discuss this later). The
Ming Dynasty, however, exemplified a
defensive posture: its westernmost expansion barely reached
Hami, while in the north, despite
Emperor Yongle’s frenzied northern campaigns against the Mongols, it never established the same dominance over the northern steppes as the
Tang Dynasty or forced nomadic empires into submission like the
Han Dynasty.
After its founding, the Ming spent most of its lifespan defending along the
Great Wall. Even shortly after Yongle’s death, the dynasty
voluntarily abandoned the Hetao region and began a decades-long contraction, relinquishing control over
Nurgan and
U-Tsang (Tibet).
Now we finally arrive at the main narrative: the
division of China into northern and southern dynasties. We can observe that nearly all such periods of division coincided with colder climatic phases—even during the
Song Dynasty, temperatures never returned to pre-divergence baseline levels.
Cold climates weakened the agrarian strength of Central Plains dynasties while forcing nomads to migrate southward more aggressively in search of survival. A weakened Central Plains state struggled to repel these nomadic incursions, while colder weather also drastically reduced rainfall in the north, triggering frequent droughts and cold spells. Even deadlier was the
Yellow River, notorious for its violent floods, which lashed the North China Plain like a whip.
Starving peasants formed migrant waves, ravaging the land like locusts—devouring grain supplies wherever they went, swelling the ranks of refugees until they overwhelmed the dynasty’s capacity to provide relief. This sparked the
largest peasant uprisings in history, with millions of angry farmers accusing the Central Plains dynasty of losing the
Mandate of Heaven and failing to protect its people. Repeated uprisings drained the dynasty’s last strength, forcing its remnants to flee southward, shrinking into the relatively stable and prosperous south.
Meanwhile, colder climates also caused
regional disparities: differences in climate led to variations in agriculture, which in turn fostered cultural divergences. This fractured the once-unified population into two (or even three, depending on whether a southern dynasty could control
Sichuan) distinct groups. The ultimate result was a deepening
north-south identity split, giving rise to the relatively stable phenomenon of
divided northern and southern dynasties.
Additionally, under colder conditions,
northern dynasties were inherently weaker than their southern counterparts. Although they controlled the
North China Plain—the empire’s demographic and agricultural core—the region’s productivity during cold periods was limited compared to the south, and in extreme cases, even became a liability. This hindered northern dynasties from leveraging their military might to swiftly conquer the south and unify the realm.
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pmc.ncbi.nlm.nih.gov
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