The Situation in 1205

Pushed east by the Jin in the previous century, the remnants of the Great Liao (Not to be confused with the Xia Dynasty) were the first of the three to face the Mongols. Temüjin launched raids on border towns in 1205, his full invasion would not begin until 1209, where the Xia would reach out to the Jin for assistance. Not wanting to assist their rival, the Jin decline, seeking to exploit the conflict to its own benefit.

"Is it not to our advantage when our enemies attack each other? Wherein lies the danger to us?" - Emperor Wanyan Yongji

Despite their significant military strength, the Xia would lose control of much of the countryside, only maintaining firm control over fortified cities. A coup put Emperor Xiangzong as ruler of the Xia, he proved to be an ineffective leader.

Faced with fortress after fortress, the Mongols often employed deception tactics to lure their enemies out into open battle. Slowly making their way towards the capital city of Zhongxing. With no way to storm the high walls and a failed attempt to flood the city, Chinggis offers peace terms which would be accepted. The Xia would become a vassal state under the Mongols, maintaining some form of autonomy.

Xi Xia would be fully annex and subjugated in two years by 1227, after failing to provide war contributions and rebelling against Mongol rule.

Surprised by the defeat and subjugation of their rival, the Jin demanded the Mongols submit and pay tribute. Refusing to do so, Chinggis planned a march on the capital of Zhongdu (more commonly known today as Beijing). The Jin however would not fall as easily as many others, with a strong military and economic might, the army took their defenses along the Great Wall. To the invaders however, the wall would prove to be no challenge, bypassing the defenses by marching or simple bribery.

With the city of Datong was placed under siege and other border towns attacked, Chinggis's march on the capital continued, the Jin Army would move to prevent the Mongols from crossing the mountain pass northwest of Zhongdu. Knowing the mountainous terrain hindered the use of cavalry warfare, the Jin stood their ground waiting for the invaders to strike. A standoff quickly developed, allowing Mongol support armies to continue rampaging and eventually out flank the Jin army, resulting in the Battle of Yehuling. With their foe dug in, the Mongols decided to employed a feigned retreat to lure their enemy out of their strong position, this proved extremely effective and the massive Jin army would move into the open where they would be completely destroyed by cavalry attacks. With the army annihilated, the road to the Zhongudu lay open.

The countryside was plundered and raided, after capturing nearby forts and slaughtering their surrendered populations (Often offering those such as academics, engineers and medical professionals mercy should they defect to their side) the Mongols would march to the capital, laying a siege where after months neither side could disperse the other, a peace treaty was agreed (Emperor Wanyan Yongji would be assassinated in a military coup, his nephew would be made Emperor Xuanzong). The Jin agreed to pay tribute and submit to the Khan's rule. Once the invaders left, the Jin quickly worked to gather the remnants of their army and relocate their capital south, towards the much more defensible city of Kaifeng, breaking the agreement. Chinggis Khan was furious when hearing this news of betrayal, he rapidly marched back.

With northern China largely abandoned, Zhongdu was surrounded and quickly stormed, the city plundered and razed for weeks, the population murdered and the Jin, limping southward, behind the protection of the Yellow River.

Chinggis Khan would leave China and turned his attention towards central Asia. In 1227, he would suffer a fall from his horse while completing the annexation of Xi Xia. Falling ill and refusing rest, he would die before the end of the year.

His son Ogedai, would be made Khan, and continue the invasion of the Jin.

The Mongols knew a crossing of the Yellow River would be difficult, lead by the legendary General Subutai, they decided to bypass the river and march from the west, then swing east to capture the Tongguan fort and march on Kaifeng. After being defeated by the Jin in battle, the Mongols tried again, swinging even further south into Song territory to bypass the fort completely. This succeeded, and Emperor Aizong (Xuanzong had been assassinated years earlier) was forced to flee his capital as it was placed under siege and later surrendered.

With another heavy lost at Kaifeng, the Jin were beaten, and the Mongols would give chase south to Caizhou. Near the Song border there was little hope of escape. After desperate pleads to the Song for assistance were refused, Emperor Aizong seeing no hope, would commit suicide during the siege, passing the throne to his general now Emperor Mo, who would go on to commit suicide less than one day later, as the final emperor of the Jin.

The Song would invade shortly before the fall of Caizhou, carving back a piece of land previously lost to the Jin. With another state falling to the Mongols, the Song remained the final independent Chinese state.

War with the Song started just one year after the fall of the Jin, their alliance now gone, the newly recovered lands quickly fell back into enemy hands. This bad news would not last long however as instability within the Mongol Empire over the succession of Ogedei Khan paused the campaign in China. The Song, taking advantage of the situation were able to capture and reinforce lost lands

With the Mongol Civil War finished and Kublai consolidating power, he quickly worked to reform many aspects of Chinese life, economics, politics, logistics, communication, army reform, were just some of his changes. His remaining territory from the massive Mongol Empire would become the new Yuan Dyansty, with it's capital of Khanbaliq (The former Jin capital).