Cavalry
They are described as Ayuddha-jivi or Shastr-opajivis (nations-in-arms), which also means that the Kamboja cavalry offered its military services to other nations as well. There are numerous references to Kambojas having been requisitioned as cavalry troopers in ancient wars by outside nations.

Mughal Empire: The Mughal armies (lashkar) were primarily a cavalry force. The elite corps were the ahadi who provided direct service to the Emperor and acted as guard cavalry. Supplementary cavalry or dakhilis were recruited, equipped and paid by the central state. This was in contrast to the tabinan horsemen who were the followers of individual noblemen. Their training and equipment varied widely but they made up the backbone of the Mughal cavalry. Finally there were tribal irregulars led by and loyal to tributary chiefs. These included Hindus, Afghans and Turks summoned for military service when their autonomous leaders were called on by the Imperial government.

European Middle Ages: As the quality and availability of heavy infantry declined in Europe with the fall of the Roman Empire, heavy cavalry became more effective. Infantry that lack the cohesion and discipline of tight formations are more susceptible to being broken and scattered by shock combat—the main role of heavy cavalry, which rose to become the dominant force on the European battlefield.
As heavy cavalry increased in importance, it became the main focus of military development. The arms and armour for heavy cavalry increased, the high-backed saddle developed, and stirrups and spurs were added, increasing the advantage of heavy cavalry even more.
This shift in military importance was reflected in an increasingly hierarchical society as well. From the late 10th century onwards heavily armed horsemen, milites or knights, emerged as an expensive elite taking centre stage both on and off the battlefield. This class of aristocratic warriors was considered the "ultimate" in heavy cavalry: well-equipped with the best weapons, state-of-the-art armour from head to foot, leading with the lance in battle in a full-gallop, close-formation "knightly charge" that might prove irresistible, winning the battle almost as soon as it began.

But knights remained the minority of total available combat forces; the expense of arms, armour, and horses was only affordable to a select few. While mounted men-at-arms focused on a narrow combat role of shock combat, medieval armies relied on a large variety of foot troops to fulfill all the rest (skirmishing, flank guards, scouting, holding ground, etc.). Medieval chroniclers tended to pay undue attention to the knights at the expense of the common soldiers, which led early students of military history to suppose that heavy cavalry was the only force that mattered on medieval European battlefields. But well-trained and disciplined infantry could defeat knights.
Massed English longbowmen triumphed over French cavalry at Crécy, Poitiers and Agincourt, while at Gisors (1188), Bannockburn (1314), and Laupen (1339), foot-soldiers proved they could resist cavalry charges as long as they held their formation. Once the Swiss developed their pike squares for offensive as well as defensive use, infantry started to become the principal arm. This aggressive new doctrine gave the Swiss victory over a range of adversaries, and their enemies found that the only reliable way to defeat them was by the use of an even more comprehensive combined arms doctrine, as evidenced in the Battle of Marignano. The introduction of missile weapons that required less skill than the longbow, such as the crossbow and hand cannon, also helped remove the focus somewhat from cavalry elites to masses of cheap infantry equipped with easy-to-learn weapons. These missile weapons were very successfully used in the Hussite Wars, in combination with Wagenburg tactics.
This gradual rise in the dominance of infantry led to the adoption of dismounted tactics. From the earliest times knights and mounted men-at-arms had frequently dismounted to handle enemies they could not overcome on horseback, such as in the Battle of the Dyle (891) and the Battle of Bremule (1119), but after the 1350s this trend became more marked with the dismounted men-at-arms fighting as super-heavy infantry with two-handed swords and poleaxes. In any case, warfare in the Middle Ages tended to be dominated by raids and sieges rather than pitched battles, and mounted men-at-arms rarely had any choice other than dismounting when faced with the prospect of assaulting a fortified position.

Islamic States: 

Arabs: The Islamic Prophet Muhammad made use of cavalry in many of his military campaigns including the Expedition of Dhu Qarad, and the expedition of Zaid ibn Haritha in al-Is which took place in September, 627 AD, fifth month of 6 AH of the Islamic calendar.
Early organized Arab mounted forces under the Rashidun caliphate comprised a light cavalry armed with lance and sword. Its main role was to attack the enemy flanks and rear. These relatively lightly armored horsemen formed the most effective element of the Muslim armies during the later stages of the Islamic conquest of the Levant. The best use of this lightly armed fast moving cavalry was revealed at the Battle of Yarmouk (636 AD) in which Khalid ibn Walid, knowing the skills of his horsemen, used them to turn the tables at every critical instance of the battle with their ability to engage, disengage, then turn back and attack again from the flank or rear. A strong cavalry regiment was formed by Khalid ibn Walid which included the veterans of the campaign of Iraq and Syria. Early Muslim historians have given it the name Tali'a mutaharrikah(طليعة متحركة), or the Mobile guard. This was used as an advance guard and a strong striking force to route the opposing armies with its greater mobility that give it an upper hand when maneuvering against any Byzantine army. With this mobile striking force, the conquest of Syria was made easy.
The Battle of Talas in 751 AD was a conflict between the Arab Abbasid Caliphate and the Chinese Tang dynasty over the control of Central Asia. Chinese infantry were routed by Arab cavalry near the bank of the River Talas.
Until the 11th century the classic cavalry strategy of the Arab Middle East incorporated the razzia tactics of fast moving raids by mixed bodies of horsemen and infantry. Under the talented leadership of Saladin and other Islamic commanders the emphasis changed to Mamluk horse-archers backed by bodies of irregular light cavalry. Trained to rapidly disperse, harass and regroup these flexible mounted forces proved capable of withstanding the previously invincible heavy knights of the western crusaders at battles such as Hattin in 1187.

Mamluks: Originating in the 9th century as Central Asian ghulams or captives utilised as mounted auxiliaries by Arab armies, Mamluks were subsequently trained as cavalry soldiers rather than solely mounted-archers, with increased priority being given to the use of lances and swords.  
Mamluks were to follow the dictates of al-furusiyya, a code of conduct that included values like courage and generosity but also doctrine of cavalry tactics, horsemanship, archery and treatment of wounds.
By the late 13th century the Manluk armies had evolved into a professional elite of cavalry, backed by more numerous but less well-trained footmen.

Maghreb: The Islamic Berber states of North Africa employed elite horse mounted cavalry armed with spears and following the model of the original Arab occupiers of the region. Horse-harness and weapons were manufactured locally and the six-monthly stipends for horsemen were double those of their infantry counterparts. During the 8th century Islamic conquest of Iberia large numbers of horses and riders were shipped from North Africa, to specialise in raiding and the provision of support for the massed Berber footmen of the main armies.
Maghrebi traditions of mounted warfare eventually influenced a number of sub-Saharan African polities in the medieval era. The Esos of Ikoyi, military aristocrats of the Yoruba peoples, were a notable manifestation of this phenomenon.

Al-Andalus: 

Iran: Qizilbash, were a class of Safavid militant warriors in Iran during the 15th to 18th centuries, who often fought as elite cavalry.

Ottoman: During its period of greatest expansion, from the 14th to 17th centuries, cavalry formed the powerful core of the Ottoman armies. Registers dated 1475 record 22,000 Sipahi  feudal cavalry levied in Europe, 17,000 Sipahis recruited from Anatolia, and 3,000 Kapikulu (regular body-guard cavalry). During the 18th century however the Ottoman mounted troops evolved into light cavalry serving in the thinly populated regions of the Middle East and North Africa. Such frontier horsemen were largely raised by local governors and were separate from the main field armies of the Ottoman Empire. At the beginning of the 19th century modernised Nizam-I Credit ("New Army") regiments appeared, including full-time cavalry units officered from the horse guards of the Sultan.

Renaissance Europe: Ironically, the rise of infantry in the early 16th century coincided with the "golden age" of heavy cavalry; a French or Spanish army at the beginning of the century could have up to half its numbers made up of various kinds of light and heavy cavalry, whereas in earlier medieval and later 17th-century armies the proportion of cavalry was seldom more than a quarter.