Carcass wrote:
Without stirrups horse and rider are, in terms of force, separate entities; lances can be used from horseback, but only by throwing or stabbing, and mounted warriors gain only height and mobility.
The generalization in the passage
In medieval times, a lance couched under the rider’s arm, unifying the force of rider and weapon, would throw its wielder backwards off the horse at impact.
An example that shows you the innovation stirrup-related
Stirrups unify lance, rider, and horse into a force capable of unprecedented violence
The phrase that is meant to show you the effect directly related to the example above
Hope this helps
Thanks yes it does.