The Tyrolean Alpine snowman is an involuntary archeological testimony to that. The professional soldier, who was a product of the first organised societies, evolved in the Near-Eastern and Mediterranean temperate climates and had to be as light on his feet as possible. The Egyptians attacked barefoot, the Romans in hobnailed sandals. The boot was still not fundamentally necessary at this point since the Assyrian infantryman wore a cuirass that reached down to his feet, the Greek hoplites had tough leggings, Roman legionaries were protected behind their long shields and the Sarmathian heavy cavalry and their horses were covered from head to toe in armour.
Everything changed when the horsemen of the Steppes brought the stirrup with them. From this moment on, the warriors of Charles Martel were better able to grip to their horses in order to charge. The boot was pushed down into the stirrup, giving the horseman a firm seat and then was covered with steel. Thenceforth the infantry was swept off the battlefields of Europe by cavalry right up until the revenge of the Flemish and English military rank and file on the French knight, at the battles of Courtrai, Poitiers, Crécy and Agincourt.
Although more modern riders became lighter so as to gain mobility against discharging weapons and then firearms, they still nonetheless kept the boot, which became more visible than ever, ending up black and shiny as part of the tasselled uniforms that were not yet required to serve as camouflage. Horse, stirrups and boots constituted the trinity of the queen of battles, which was brought to its tactical apogee by Napoleon.
However, the combination of fire and motor allowed the inexorable rise of the assault tank, which proved so decisive in concluding the Great War. While the lesson was forgotten by those who invented it, the German officer corps, despite its already anachronistic bootwearing, ended up replacing the horse with the armoured division. Finally the particularly laid-back attitude of the American soldiers liberating Europe ultimately led to the boot being ousted from the practical arena of war. Although nostalgic dictators of Latin America and the troops of communist states still parade in boots, their operational use is nowadays limited to the cold climates from whence they came.