The first invasion, of 1211, was probably not made in much strength. It passed through the wall without difficulty, one of the entrances being opened by treachery, and dispersed the advanced forces of the empire. Then one of the Kin armies was trapped in hill country which it knew less well than the invaders, and Chepe's touman, making a night march round and on to its rear, broke it up. But as the invaders penetrated deeper they found the fortified cities an almost insuperable obstacle both to their methods and to their small numbers, and, in face of the growing strength of the enemy forces, withdrew in the autumn. Next spring this invasion was renewed and this time Jenghiz Khan appears to have used Taitong-Fu as a bait, in the same way as Bonaparte used the fortress of Mantua in I796—to draw on and annihilate the successive armies which came to its relief. But the reduction of fortified cities remained an obstruction until the campaign of 1214. Then a vast con centric advance by three armies, the centre one moving on to the sea in the rear of Yen-Kin, the Kin capital, brought about such a demoralization that the emperor fled to the south and the chaos in his dominions enabled the Mongols to subdue the disorganized fragments. Leaving his general Mukhuli in control in China Jenghiz Khan himself returned to Karakorum. With his borders now firmly established as far as the river barrier of the Hoang-Ho, his base was secure for an advance towards the west. Here lay the rich and fertile empire of the Shah of Khwarizm (Karismian empire), which embraced what is to-day Turkistan, Persia, and northern India. The Shah's intrigues, combined with Jenghiz Khan's desire for expansion, brought about a conflict, the signal for which was the Shah's folly in putting to death the envoys of Jenghiz.
Then, early in 1220, Jenghiz Khan struck his opening blow, a shrewdly conceived diversion. Chepe, with two toumans, had passed by the southern route from Kashgar into Fergana, and was advancing on Khojent, which covered the southern end of the Syr Daria line. Thus Chepe directly threatened the Shah's right flank, as well as Samarkand and Bukhara, which lay beyond —the two centres of his power. It was a dagger pointing at the heart of the enemy. The Shah reinforced the Syr Daria line, and concentrated some 40,000 at Bukhara, and also at Samar kand. Against this Karismian total of some 200,000 men the Mongols had probably about 150,000 in the invading armies.
Jenghiz Khan had distributed his main striking force into three armies, two under his sons Juji and Jagatai. While Chepe was striking his first blows in Fergana, the three armies which formed the main force traversed a northern route by the Dzungarian Gate, and in February suddenly debouched on the left flank of the Syr Dada line. The two armies of Juji and Jagatai turned
south from Otrar, clearing the line of the Syr Daria, capturing the fortresses, and working towards Chepe's detachment, which, after taking Khojent, was seeking to join hands with them. Then, like a thunder-clap, as the Shah's attention was fixed to his front, the news reached him that Jenghiz Khan with his mass of manoeuvre had appeared on his left rear, and was almost at the gates of Bukhara.
This army of 40.000 men, under Jenghiz Khan himself, had followed in the wake of Juji's and Jagatai's armies, crossed the Syr Daria at Otrar, and then disappeared. Masked by the armies of the two princes, its arrival on the scene had passed almost unnoticed. Having crossed the Syr Daria, it vanished into the immense desert of Kizyl-kum. By this dramatic venture of 40,000 to 50,000 men, and even more horses, across a desert, Jenghiz Khan appears to have gained complete secrecy until the moment when he debouched at the southern end and was almost on the top of Bukhara—in rear of the Shah's armies ! At one blow the Shah's whole line was turned, and his communications severed with his more distant westerly States, whose forces had still to arrive. Demoralized, the Shah fled and left the garrison of Bokhara to its fate.
Jenghiz Khan captured Bukhara, and then turned east towards Samarkand. Meanwhile, the armies of the princes had joined hands with Chepe, and were converging on Samarkand. The doomed last stronghold of the Karismian power was caught be tween the hammer of the princes and the anvil of Jenghiz Khan himself, and soon fell. In the brief space of five months Jenghiz Khan had overthrown the mighty Karismian empire, and opened the gateway to the west, towards Russia and towards Europe.
The enemy armies crushed, Jenghiz Khan despatched Sabutai and Chepe westwards in pursuit of the Shah and to open up the path to further conquests. The Shah's son, Jelaladdin, still held out in the south for a time, and then crossed the Indus. Jenghiz followed him up, and in 1221 sent an expedition to Delhi. which took nominal possession of the country that his successors were to hold in reality. Jenghiz devoted his remaining years until his death to consolidating his mighty empire, which stretched from Korea to the Persian gulf.