More peasants had more access to horses, which gave them more mobility. This had several important implications. First, farmers could now get to the market on their own where ordinarily they would be reliant on merchants. Effectively this reduced shipping costs for farmers and made their whole operation more profitable. Further democratizing transportation were improved wagons. Up to now, these had been two wheeled, but by the 13th century, a four wheeled version emerged. Whippletrees allowed multiple animals to pull heavier plows, pivoted front axles greatly increased maneuverability and adequate brakes were increasingly available.

These changes allowed peasants to farm land further from a river — the highway system of the Middle Ages. This in turn meant more farms in the land, and an increase to general carrying capacity. An increase in population is highly associated with prosperous times (the contra positive holds). A second benefit of horse-based mobility were more living options. Now peasants could live in larger towns and ride to their farm every morning to do their day’s work, then return to their town. This increased their prosperity in many ways, giving them access to schools for their children, more power to self-govern via communes, access to culture, pubs, and other amenities found in a Medieval towns.

graph TD
DH[Draft horses] --> |Used for transport| PM[Peasant mobility]
PM --> |Cut out merchants| CT[Cheap transport]
PM --> |Commute on horseback| TS[Town size]
TS --> |City scale benefits| PP[Peasant prosperity]
CT --> |Less spent on transport| FP[Farm profits]
CT --> NF[Farm distance from rivers]
NF --> |More food production| CC[Carrying capacity]
FP --> PP
CC --> PP
FY[Farm Yields] --> PP

style Inventions fill:yellow,stroke:#333,stroke-width:4px
Inventions[Four wheeled wagons<br/>Whippletrees<br/>Pivoted front axles] --> PM

Source: Medieval Technology and Social Change by Lynn White