What role does join-up play in starting young horses according to Monty Roberts?

Monty Roberts is the originator of join-up, a concept that has influenced virtually every modern natural horsemanship trainer including Clinton Anderson, Pat Parelli, and Warwick Schiller, even when they use different terminology. Understanding Roberts' original work on join-up is essential background for anyone working with young horses because it explains the behavioral mechanism that all round pen work is designed to activate. Join-up is based on Roberts' observation of wild horse herd behavior — specifically the way a dominant mare uses body language to drive a young or disobedient horse out of the herd, and the signals the driven horse uses to communicate submission and a request to return. In the wild, a horse driven from the herd by the dominant mare will eventually stop, lower its head, and chew — signals that it is releasing its adrenaline and asking to come back. The mare then turns away from the horse, presenting her shoulder rather than her driving eye, and the horse walks up and joins with her. Roberts replicated this in the round pen with domestic horses, using specific body language — squared shoulders and direct eye contact to drive, turning sideways and dropping the eyes to invite. He discovered that horses almost universally respond to the invitation to join within two to ten minutes of the driving phase, and that after join-up a young horse stands quietly, follows at liberty, and accepts handling including saddling and backing with significantly less resistance than horses prepared through traditional methods. Clinton Anderson's hook-on is a direct derivative of Roberts' join-up. Parelli's Friendly Game incorporates the same principle. Schiller's emphasis on waiting for the horse to choose the handler as a safe base reflects the same understanding. Roberts' contribution to the field of colt starting is foundational, and his book 'The Man Who Listens to Horses' remains required reading for anyone serious about starting young horses without force.