Black leather and black leather shoes have been around longer than we can reliably understand. While there is no specific single lineage for black leather boots, among the earliest and most prominent adopters of the modern black boot can be traced to cavalrymen and military officers of the 18th century. These earliest designs were sometimes called Hessian boots, after the German mercenaries who popularized their use. These later became the part of standard officer uniforms in much of continental Europe.
In a classic case of form following function, black leather made it easier to create a consistent color across many pairs in a pre-industrial time. Even if the leather was sourced from different tanneries and the boots were built in different workshops, there was a higher likelihood of matching similar colors. From a use standpoint, black doesn’t reflect light the way other shades do, making it ideal for hard wear because you don’t need to pamper the leather. Maintenance is also a breeze, since there are so many easy ways to darken and re-dye the leather. For occasions with more formality, black leather takes equally well to a shine, which makes it possible to “upgrade” a normal boot for special occasions as well.