Horses in warfare
On the European continent, the need to carry more armour against mounted enemies such as the Lombards and Frisians led to the Franks developing heavier, bigger horses. As the amount of armour and equipment increased in the later Middle Ages, the height of the horses increased; some late medieval horse skeletons were of horses over 1.5 metres (15 hands).
Stallions were often used as destriers due to their natural aggression. However, there may have been some use of mares by European warriors, and mares, who were quieter and less likely to call out and betray their position to the enemy, were the preferred war horse of the Moors, who invaded various parts of Southern Europe from 700 AD through the 15th century. Geldings were used in war by the Teutonic Knights, and known as "monk horses" (German: Mönchpferde or Mönchhengste). One advantage was if captured by the enemy, they could not be used to improve local bloodstock, thus maintaining the Knights' superiority in horseflesh.

Uses: The heavy cavalry charge, while it could be effective, was not a common occurrence. Battles were rarely fought on land suitable for heavy cavalry. While mounted riders remained effective for initial attacks, by the end of the 14th century, it was common for knights to dismount to fight, while their horses were sent to the rear, kept ready for pursuit. Pitched battles were avoided if possible, with most offensive warfare in the early Middle Ages taking the form of sieges, and in the later Middle Ages as mounted raids called chevauchées, with lightly armed warriors on swift horses.

The war horse was also seen in hastiludes – martial war games such as the joust, which began in the 11th century both as sport and to provide training for battle. Specialised destriers were bred for the purpose, although the expense of keeping, training, and outfitting them kept the majority of the population from owning one. While some historians suggest that the tournament had become a theatrical event by the 15th and 16th centuries, others argue that jousting continued to help cavalry train for battle until the Thirty Years' War.

Transition: The decline of the armoured knight was probably linked to changing structures of armies and various economic factors, and not obsolescence due to new technologies. However, some historians attribute the demise of the knight to the invention of gunpowder, or to the English longbow. Some link the decline to both technologies. Others argue these technologies actually contributed to the development of knights: plate armour was first developed to resist early medieval crossbow bolts, and the full harness worn by the early 15th century developed to resist longbow arrows. From the 14th century onwards, most plate was made from hardened steel, which resisted early musket ammunition. In addition, stronger designs did not make plate heavier; a full harness of musket-proof plate from the 17th century weighed 70 pounds (32 kg), significantly less than 16th century tournament armour.
The move to predominately infantry-based battles from 1300 to 1550 was linked to both improved infantry tactics and changes in weaponry. By the 16th century, the concept of a combined-arms professional army had spread throughout Europe. Professional armies emphasized training, and were paid via contracts, a change from the ransom and pillaging which reimbursed knights in the past. When coupled with the rising costs involved in outfitting and maintaining armour and horses, the traditional knightly classes began to abandon their profession. Light horses, or prickers, were still used for scouting and reconnaissance; they also provided a defensive screen for marching armies. Large teams of draught horses or oxen pulled the heavy early cannon. Other horses pulled wagons and carried supplies for the armies.

Early modern period: During the early modern period the shift continued from heavy cavalry and the armoured knight to unarmoured light cavalry, including Hussars and Chasseurs à cheval. Light cavalry facilitated better communication, using fast, agile horses to move quickly across battlefields. The ratio of footmen to horsemen also increased over the period as infantry weapons improved and footmen became more mobile and versatile, particularly once the musket bayonet replaced the more cumbersome pike. During the Elizabethan era, mounted units included cuirassiers, heavily armoured and equipped with lances; light cavalry, who wore mail and bore light lances and pistols; and "petronels", who carried an early carbine. As heavy cavalry use declined armour was increasingly abandoned and dragoons, whose horses were rarely used in combat, became more common: mounted infantry provided reconnaissance, escort and security. However, many generals still used the heavy mounted charge, from the late 17th century and early 18th century, where sword-wielding wedge-formation shock troops penetrated enemy lines, to the early 19th century, where armoured heavy cuirassiers were employed.

Light cavalry continued to play a major role, particularly after the Seven Years' War when Hussars started to play a larger part in battles. Though some leaders preferred tall horses for their mounted troops this was as much for prestige as for increased shock ability and many troops used more typical horses, averaging 15 hands. Cavalry tactics altered with fewer mounted charges, more reliance on drilled maneuvers at the trot, and use of firearms once within range. Ever-more elaborate movements, such as wheeling and caracole, were developed to facilitate the use of firearms from horseback. These tactics were not greatly successful in battle since pikemen protected by musketeers could deny cavalry room to manoeuvre. However the advanced equestrianism required survives into the modern world as dressage. While restricted, cavalry was not rendered obsolete. As infantry formations developed in tactics and skills, artillery became essential to break formations; in turn, cavalry was required to both combat enemy artillery, which was susceptible to cavalry while deploying, and to charge enemy infantry formations broken by artillery fire. Thus, successful warfare depended in a balance of the three arms: cavalry, artillery and infantry.
As regimental structures developed many units selected horses of uniform type and some, such as the Royal Scots Greys, even specified colour. Trumpeters often rode distinctive horses so they stood out. Regional armies developed type preferences, such as British hunters, Hanoverians in central Europe, and steppe ponies of the Cossacks, but once in the field, the lack of supplies typical of wartime meant that horses of all types were used. Since horses were such a vital component of most armies in early modern Europe, many instituted state stud farms to breed horses for the military. However, in wartime, supply rarely matched the demand, resulting in some cavalry troops fighting on foot.

19th century: In the 19th century distinctions between heavy and light cavalry became less significant; by the end of the Peninsular War, heavy cavalry were performing the scouting and outpost duties previously undertaken by light cavalry, and by the end of the 19th century the roles had effectively merged. Most armies at the time preferred cavalry horses to stand 15.2 hands (62 inches, 157 cm) and weigh 990 to 1,100 pounds (450 to 500 kg), although cuirassiers frequently had heavier horses. Lighter horses were used for scouting and raiding. Cavalry horses were generally obtained at 5 years of age and were in service from 10 to 12 years, barring loss. However losses of 30–40% were common during a campaign due to conditions of the march as well as enemy action. Mares and geldings were preferred over less-easily managed stallions.
During the French Revolutionary Wars and the Napoleonic Wars the cavalry's main offensive role was as shock troops. In defence cavalry were used to attack and harass the enemy's infantry flanks as they advanced. Cavalry were frequently used prior to an infantry assault, to force an infantry line to break and reform into formations vulnerable to infantry or artillery. Infantry frequently followed behind in order to secure any ground won or the cavalry could be used to break up enemy lines following a successful infantry action.
Mounted charges were carefully managed. A charge's maximum speed was 20 km/h; moving faster resulted in a break in formation and fatigued horses. Charges occurred across clear rising ground, and were effective against infantry both on the march and when deployed in a line or column. A foot battalion formed in line was vulnerable to cavalry, and could be broken or destroyed by a well-formed charge. Traditional cavalry functions altered by the end of the 19th century. Many cavalry units transferred in title and role to "mounted rifles": troops trained to fight on foot, but retaining mounts for rapid deployment, as well as for patrols, scouting, communications, and defensive screening. These troops differed from mounted infantry, who used horses for transport but did not perform the old cavalry roles of reconnaissance and support.

Sub-Saharan Africa: Horses were used for warfare in the central Sudan since the 9th century, where they were considered "the most precious commodity following the slave." The first conclusive evidence of horses playing a major role in the warfare of West Africa dates to the 11th century when the region was controlled by the Almoravids, a Muslim Berber dynasty. During the 13th and 14th centuries, cavalry became an important factor in the area. This coincided with the introduction of larger breeds of horse and the widespread adoption of saddles and stirrups.