The main reason is not complicated is that both Xiang Yu and Napoleon are in multiple strategic directions while setting up strong enemies.
Xiang Yu
In the first stage, Xiang Yu faced enemies in two directions: the King of Han and the State of Qi. The six states of Shandong surrendered without a fight in the war of unification of the Qin dynasty was the state of Qi. It shows that the will to resist the king of Qi Jian was extremely weak, but at the same time, Qi land retained the most vitality. And its economy was not seriously damaged.
In contrast to Qi, Korea, Wei, Zhao, and Yan all suffered heavy losses in the Qin unification war, and their important cities and towns were crippled and their economies withered. Therefore, after the start of the Great Revolt against Qin, Wei, Zhao, Korea, and Yan were economically weak. The newly built armies were not much stronger than the militia and were often defeated by Liu Bang’s elite troops (equivalent to the new Qin army).
On the other hand, Qi had an entire city, a surviving economy, and a high degree of loyalty, which allowed Qi to organize a more capable army that could withstand Xiang Yu’s attacks for a long time. Even if Xiang Yu took important areas, Qi could use movement and guerrilla warfare to consume Xiang Yu’s army and make them fall into a quagmire.
The first stage of the Chu-Han War
The first phase of the Chu-Han War was when Xiang Yu was trapped in Qi, and Liu Bang took the opportunity to consolidate the newly occupied San Qin and led a coalition of lords to capture the capital of Chu, Pengcheng.
The first phase ended with Xiang Yu’s return to Pengcheng and the defeat of Liu Bang’s allied army, the disintegration of the allied forces of the vassals against Xiang, and Liu Bang’s retreat to Xingyang to stabilize the battle line. Therefore, the first stage of the Chu-Han War was when Qi tripped up Xiang Yu’s main force, and Liu Bang took the opportunity to grow bigger. In other words, Qi acted as the anvil, and the Han army became the hammer.
In the second stage, Liu Bang personally led his troops to resist Xiang Yu’s main force at Xingyang, while Han Xin attacked Wei, Zhao, Korea, and Qi, creating a pincer movement against Xiang Yu. Liu Bang used the general mobilization mechanism that the Qin population used to + the natural danger of Qin land to hold back the main Chu army.
The elite Han army led by Han Xin formed a descending blow to the nascent armies of Wei, Zhao, and Korea, quickly destroyed Han, Zhao, and Wei, and advanced to the land of Qi. Xiang Yu sent Long and led part of his main force to save Qi to prevent Qi from being destroyed, causing Han’s army to have an absolute advantage.
As a result, Han Xin killed Long He at Weishui and eliminated a considerable part of Chu’s mobile force. The state of Qi was greatly wounded by the two massive attacks of Chu and Han and was overrun by Han Xin in one fell swoop.
Since Liu Bang controlled most of the world and its population, and Han Xin could break Pengcheng from Qi at any time, the defeat of Xiang Yu was inevitable.
The defeat of Xiang Yu
The defeat of Xiang Yu was, on the one hand, since Liu Bang did not decisively ease the conflict with Qi after capturing the three Qin states and making Liu Bang his main enemy.
On the other hand, it was because he lacked the talents under his command who could lead the three armies like Han Xin and could not divide his troops between competing with Liu Bang for the three Jin dynasties, which led to Liu Bang’s absolute advantage.
Napoleon
Napoleon also had the same problem. After he implemented the continental blockade policy, he became enemies with Britain and Russia at the same time. Britain’s economic strength was extremely strong, and every anti-French alliance was financed by British money.
Britain’s naval strength was the highest in the world, + the fact that it occupied the English Channel, made it impossible for the French to strike the British mainland. On the other hand, with its large population, great strategic depth, and growing strength since Peter the Great’s reforms, Russia was an extremely difficult enemy to deal with.
Britain’s offshore balancing strategy fundamentally conflicted with France’s national interests. It should be ranked as the primary enemy, while France’s conflict with Russia could be moderated to some extent.
Napoleon did well at first, defeating the British-backed Austro-Hungarian Empire and Prussia, leaving Britain with no agent on the continent to confront France. But then Napoleon mistakenly launched a war of conquest against Spain, plunging a significant portion of his forces into the quagmire that was Spain (in which Britain had sent a large army to fight directly).
Before Spain was unsettled, Napoleon summoned another 600,000 troops to attack Russia, thus fighting two powerful opponents, Britain and Russia, simultaneously.
Due to Russia’s great strategic depth and Kutuzov’s tactics of clearing the field, the French offensive momentum was exhausted after the capture of Moscow. The French army was forced to withdraw after being cut off from supplies during the harsh Russian winter and lost more than half of its best troops to Russian pursuit.
In Spain, the French army was defeated by the Anglo-Spanish alliance and was forced to withdraw to France, losing many of its best men. After the defeat of these two wars, Napoleon lost the majority of his elite, and the countdown to his demise was on.
Napoleon’s defeat
On the one hand, Napoleon’s defeat was because he was the enemy of both Britain and Russia, and he opened up two unfavorable battlefields, Spain and Russia.
On the other hand, France failed to reform its financial system. It could not issue a large number of bonds with a lower interest rate to support the long-term war like Britain did. The national strength was depleted drastically with the prolongation of the war, which finally led to the defeat.