Additionally, did they recruit settled peoples other than the siege engineers from China?
By the conquest of China, most troops serving Mongol Khans were probably not ethnic Mongols. This was certainly the case in China, where Kublai Khan established both the "Han Army" of ethnic Chinese and the "Newly Submitted Army" of former Song soldiers who defected. While exact numbers varied over time and are impossible to ascertain, the army almost certainly consisted of more Chinese than Mongols. The roving hordes still existed, especially in the Northern part of the empire. However, they formed an elite core of the Yuan army, while the bulk were Chinese.
In the West, things were far more complicated. Unlike in the East, where nomadic Mongols clashed with settled Chinese civilization, the Eurasian Steppe to the West had been home to dozens of nomadic Turkic empires. Turkic nomads had been politically ascendant in the area for centuries before the Mongol Conquest. The Mongols thus found themselves as a militarily superior, dominant group among a sea of peoples - many of whom were nomads who shared many of their same traditions.
Because of this, what it meant to be "Mongol" in the West gradually became diluted, as Mongols and Turks interbred, assimilated, and adopted similar cultural practices. Scholars have started to call all the Mongol governments West of the Altai mountains "Turko-Mongol" regimes. Neumann and Wigen:
The problem in determining Mongol influence is that much of the areas ruled by Mongols were ruled by Turks both before and after Mongol domination. And since Turkic and Mongol political traditions are so heavily intertwined and thus similar, it is almost impossible to tell what is a Mongol influence and what is a Turkic influence when it comes to political institutions and traditions.
This mutual assimilation happened multiple ways, both peaceful and violent. In the Golden Horde, for example, local Turks were first employed to help govern:
When Batu died in 1256, he had built a tent capital in Saray on the Volga (100 km north of today’s Astrakhan) for his Khipchak Khanate, which came to be known locally as the Golde Horde.
Since the steppe-dwelling Mongols lacked expertise in running administrative apparatuses, throughout the Mongol Empire these were mostly staffed locally. In the case of the Khipchak Khanate, however, there was little by way of local administrative personnel to be found, and so the khagan relied on Khwarazm Turks (in Russian Besserminy). The Khipchak Khanate adopted Islam as its official religion under Özbek (1313-1341), in conjunction with which they also adopted the Persian administrative diwan system.
Out of this symbiosis, an entirely new hybrid ethnic group emerged:
The mix of Turko-Mongol, and also some Persian, elements was also pronounced amongst this dominant layer of population, which came to be known as Tatar.
In other areas, the transition from a pure Mongol Empire to a Turko-Mongol empire was more violent.
In the Chagatai Khanate in Central Asia, two halves developed: the West was Islamic, and largely settled and agricultural. The East was Tengrist and clung to Mongol nomadic traditions. Civil war therefore pervaded, pitting the Turko-Mongol West against the Mongol East. The civil war ended when Mongol warlord Ilyas Khosa was defeated by Turko-Mongol warlord Timur the Lame.
Timur himself embodied the new elite that rose out of the ashes of the violent Mongol conflicts. Genetically, his Barlas tribe were Mongolian, descendants of warriors who arrived with Genghis Khan. Culturally, however, they were Turkic - converts to Islam, following Turkic customs and practices.
As mentioned above, it was easy for these two groups to integrate - both were nomadic, both travelled in hordes, both could adapt to the Mongol way of warfare. In the West, "Mongol", "Tartar", and "Turk" became blurred terms, so much so that to Westerners they were used interchangeably.
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