Perhaps the technological change that most impacted the way war was waged leading up to 1800 was the development and improvement of firearms. Prior to the fourteenth century, rudimentary firearms were only very occasionally seen on the battlefield. However, as time went on, the reliability and portability of these weapons improved. These technological changes were not a sudden development. Over the centuries, firearms were usually used in tandem with more traditional weapons like pikes and halberds. Yet by the eighteenth century, exploding projectiles from canons, flintlock muskets, and rifling meant that the nature of warfare was vastly different than it had been and tactics had to change in kind.
With artillery that could topple castle walls, the nature of sieges changed. Armies began engaging in the field more often than from behind fortifications. Consequently, armies became more nimble and diverse. In the early seventeenth century, King Gustavus Adolphus of Sweden combined artillery with pikemen, archers, cavalry, and musketeers to create a fighting force that could outmatch its opponents, who relied on a more homogenous mix of fighters.
Because even the most rudimentary firearms are still more complex and expensive than pikes and spears, the makeup and organization of armies had to adapt. Instead of recruiting farmers and peasants in times of war, professional armies became more common. Tactics could then become more formalized and complex to take advantage of the new technologies. For instance, successive linear lines of musketeers allowed soldiers to concentrate their fire and reload while pikemen defended them against cavalry attacks. Of course, this and other maneuvers required training and practice, something that could best be achieved by maintaining standing professional armies. Also, as firearms became more portable, fighting units were divided into smaller formations to become more nimble on the battlefield. The need for more professional soldiers led to the establishment of military academies throughout Europe. By 1800, professional and well-trained armies had become the norm in Europe.