in western Europe the 15th century opened with the final half of the Hundred Years' War between England and France. what had begun with the flowery last vestiges of chivalry still in fashion--in the royal court, if not so much on the battlefield--was now a war fought by professional soldiers and paid mercenaries. armies were a diverse mix of armored knights, infantry armed with a wide variety of pole arms, crossbows, longbows, and primitive handguns.

Crecy and Poitiers proved the end of the dominance of armored cavalry as the singular deciding arm, and as the 1300s ended and the 1400s began, infantry and artillery were the new kings and queens of the battlefield. yeoman archers had felled the knights, and gunpowder cannons had felled their castles.

large infantry and gunpowder armies cost a lot of money, so the only forces that could compete in this new dawning age of warfare were those with access to huge sums of ready cash. a small local lord could no longer defy his master from behind his provincial castle walls. decentralized "feudal" European kingdoms were undergoing a transformation into powerful centralized states.

in the mid to late 15th century the polity that had the most wealth and coincidentally, the most advanced siege train of Europe, was Duke Philip of Burgundy. by force or inheritance he had accumulated a vast realm that stretched from the North Sea to the valley of the Rhone, through modern Netherlands, Belgium, Germany, France, and Switzerland. Philip used his vast wealth to easily bombard his rivals into submission, and the monarchs of Europe took notice.

in 1494 the French king invaded Italy, kicking off a half-century of conflicts known as the Italian Wars. he brought with him a huge siege train of artillery and thousands of mercenaries equipped with pikes and primitive handguns called arquebuses.

the Italian Wars saw a rapid revolution in military tactics and technology. the most visually transformative were the huge new star-shaped fortresses that sprung up all over the peninsula. these new fortifications had low sloped walls to deflect cannonballs and their star-shaped outlines were designed with mathematically calculated angles to maximize interlocking zones of fire.

the Italian Wars were dominated by sieges, but in open field battles the hand held firearm was growing increasingly dominant. it was the Spanish who developed the next great revolution in army tactics and composition--the feared tercios were squares of pike-armed infantry supported by detachments of arquebusiers that marched across the battlefield like an unstoppable force for the next century. after the Italian Wars petered out in 1559, the next major international conflict to scar the face of Europe was fought between the Imperial Spanish and their rebellious Protestant subjects of the Dutch Netherlands. the '80 Years' War' of Dutch independence blurred later into the sectarian conflicts in religiously fragmented Germany in the 'Thirty Years' War' of 1618-1648.

it was of course then, naturally, the Dutch who developed the next evolutionary phase of European military tactics. Dutch general Maurice of Nassau took inspiration from ancient Roman military writers like Vegetius and introduced the beginnings of drill and complex marching evolutions that would be the later hallmark of European gunpowder armies of the 18th and 19th centuries. in the first half of the 17th century Nassau and Swedish General King Gustavus Adolphus are credited with increasing the proportion of guns to pikes in their armies, thinning their battle formations from the thick checkerboard squares of the tercios to long lines of arquebusiers, musketeers, and cannons only sparsely reinforced with blocks of pikemen.

in the late 1600s the invention of the bayonet allowed armies to do away with the pike altogether. the once heterogeneous and diverse armies of late medieval Europe had transitioned over three centuries into largely uniform armies of infantry armed with muskets and bayonets.

this is a very brief and frankly partially academically outdated narrative that is nonetheless accurate in describing the most visible changes of European militaries from the late middle ages through the Renaissance and the Early Modern era.

Geoffrey Parker, The Military Revolution: Military Innovation and the Rise of the West, 1500-1800

Geoffrey Parker, The Army of Flanders and the Spanish Road

William H. McNeill. The Pursuit of Power: Technology, Armed Force, and Society since A.D. 1000