Explanation: In medieval Europe, warfare had largely been reshaped in the post-Classical period by the advent of ever-more-numerous and ever-stronger fortifications, which we generally refer to as 'castles'. These fortifications allowed small groups of elites to impose their will on a broad swathe of the countryside, slow invading foes for months at a time, and cut enemy supply lines if they were left to their own devices.

When Muslims in Spain introduced gunpowder to Christian Europe in the 14th 13th century AD, Europe eagerly began constructing cannons and blowing down all of their fancy castles, eventually causing a radical shift in the nature of European warfare by the 16th century AD. Fortifications became increasingly secondary to massive professional armies and artillery corps, and the influence of elite warrior-knights faded in both military and political terms.