Question: Who made a threat that was responsible for China expanding into the Ordos reigon?
About the article "Archery", section "Mounted archery".

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The Ordos (Mongolian Cyrillic: Ордос) are a Mongol subgroup that live in Uushin district, Inner Mongolia.
Ordos literally means plural of Ordo.
The Three Tribes of Uriyangkhaid, Tümed in north Shanxi, Ordos Mongols in Ordos and north of Shensi extended southward beyond the Ming defense zone in the 14-15th centuries.
Since 1510, the Ordos were ruled by descendants of Batumongke Dayan Khan.
The Ordos Mongols believe that they have been responsible for the shrine of Genghis Khan since their inception.
However, the modern place where mausoleum of Genghis Khan located is inhabited by the Darkhads because the Ordos Mongols were forced to be resettled outside Ordos grasslands.
Traditionally, Ordos territory is divided into 7 banners.
Their number reached 64,000 in 1950 and a possible current estimate of the Ordos people might be less than 100,000. 
The Mentat who assists the player in "Dune 2000".
He is rumored to be a thinking machine of Ixian design, traded to the Ordos in exchange for a fortune in Melange.
If so, the fact that he is a man interfaced with a machine would allow its existence, as it is not "a machine in the likeness of a human mind".
Edric O could temporarily place his consciousness into a storage medium while his body was incapacitated and could communicate via a visual monitor, as evidenced by one of the "Dune 2000" cut-scenes.
The Ix implanted a listening device in a knob on a mechanism in Edric O's head and presented its receiver to the Padishah-Emperor.
Edric discovered its presence and deactivated it, demonstrating that he was loyal to Ordos rather than Ix.
His later increasing use of melange spice expanded his abilities greatly but made him seem unstable, intoxicated by his new-found prescience.
It enabled him to see a potential future in which all of the other factions would be set against each other, acted in a manner that made this future come to pass, and predicted the narrow window of probability when they would be at their weakest so Ordos forces could strike decisively.
He might have been eliminated by the Ordos, either because he was viewed as a threat or because his prescience overcame him and made him useless. 
In 215 BCE, Qin Shi Huangdi ordered General Meng Tian to set out against the Xiongnu tribes, situated in the Ordos region, and establish a frontier region at the Ordos Loop.
Believing that the Xiongnu were a possible threat, the emperor launched a preemptive strike against the Xiongnu with the intention to expand his empire.
In 215 BCE, General Meng Tian succeeded in defeating the Xiongnu and driving them from the Ordos region, then he seized their homeland.
After the catastrophic defeat at the hands of General Meng Tian, the Xiongnu leader Touman was forced to flee far into the Mongolian Plateau.
As a result of the northward expansion, the threat that the Qin empire posed to the Xiongnu ultimately led to the reorganization of the many tribes into a confederacy.
General Meng Tian was instructed to secure the frontier with a line of fortifications, which would become known as the Great Wall of China.
Fusu (Prince of Qin) and General Meng Tian were stationed at a garrison in Suide and soon began with the construction of the walled defenses, which would be connected with the old walls from the Qin, Yan, and Zhao states.
The Qin walls ran from Liaodong to Lintao, thus enclosing the conquered Ordos region. 
Central Asian tribesmen (after the domestication of the horse) and American Plains Indians (after gaining access to horses) became extremely adept at archery on horseback.
Lightly armoured, but highly mobile archers were excellently suited to warfare in the Central Asian steppes, and they formed a large part of armies that repeatedly conquered large areas of Eurasia.
Shorter bows are more suited to use on horseback, and the composite bow enabled mounted archers to use powerful weapons.
Empires throughout the Eurasian landmass often strongly associated their respective "barbarian" counterparts with the usage of the bow and arrow, to the point where powerful states like the Han Dynasty referred to their neighbours, the Xiong-nu, as "Those Who Draw the Bow" For example, Xiong-nu mounted bowmen made them more than a match for the Han military, and their threat was at least partially responsible for Chinese expansion into the Ordos region, to create a stronger, more powerful buffer zone against them.
It is possible that "barbarian" peoples were responsible for introducing archery or certain types of bows to their "civilized" counterparts—the Xiong-nu and the Han being one example.
Similarly, short bows seem to have been introduced to Japan by northeast Asian groups.
An early reference to the Xiongnu was by Sima Qian who wrote about the Xiongnu in the "Shiji" ( BCE), drawing a distinct line between the settled Huaxia people (Chinese) to the pastoral nomads (Xiongnu), characterizing it as two polar groups in the sense of a civilization versus an uncivilized society.
Sources from the pre-Han eras often classified the Xiongnu as the Hu people, even though this was more a blanket term for nomadic people in general; it only became an ethnonym for the Xiongnu during the Han.
Ancient China often came in contact with was described as the "Hsien-yün" and the "Jung" nomadic people.
In later Chinese historiography, some groups of these peoples were believed to be the possible progenitors of the Xiongnu people.
These nomadic people often had repeated military confrontations with the Chinese dynasties of the Shang and especially the Zhou, who often conquered and enslaved the nomads in an expansion drift.
During the Warring States period, the Chinese armies from the Qin, Zhao, and Yan states were encroaching and conquering various nomadic territories that were inhabited by the Xiongnu and other Hu peoples.
The Chinese Qin empire was set on preemptively attacking the Xiongnu and expanding their territory at the expense of the Xiongnu.
In 215 BC, Qin Shi Huang sent General Meng Tian to conquer the Xiongnu and drive them from the Ordos region, which he did later that year.
After the catastrophic defeat at the hands of General Meng Tian, the Xiongnu leader Touman was forced to flee far into the Mongolian Plateau.
The Qin empire became a threat to the Xiongnu, which ultimately led to the reorganization of the many tribes into a confederacy.