High medieval Europe could support large armies when circumstances demanded them, as campaigns associated with the First Crusade, Barbarossa, the Mongols, and the Reconquista demonstrate. Castle-dense warfare often made smaller forces sufficient because roughly 3,000 troops could besiege a fortress without the supply burden of 30,000. Disease was a major killer in siege camps, which made smaller armies easier to sustain as well as easier to keep healthy. More open theatres in the Middle East and China encouraged larger forces, especially when replacements would have to cross great distances. Population, fortification patterns, and reinforcement routes explain the different army sizes better than a simple claim that medieval Europe lacked capacity.
Notable Point · 5:05:17-5:07:49
Castle warfare often made smaller medieval armies the rational choice
A comparison of medieval theatres explains army size through fortifications, disease, population, and reinforcement distance rather than assumed European incapacity.