Highlights 4000 men were from the Stanley family. They were known have the tendency to change sides during battle , & King Richard did not trust them. So to prevent The Stanley's from changing sides, King Richard imprisoned the first son -Strange & sent word to his father that if he turned traitor his son will be beheaded.
At the critical moment, Sir William Stanley's army attacked Richard, seemingly coming to the aid of Henry. As the royal body watch their main army source turn to their enemy's side, they lost confidence and start to crumble.
Lord Stanley, therefore declaring him the new king, places the crown on Henry's head. Henry was famous for leading a rebel force & defeating a royal army more than twice its size, placing himself on the throne as the first of the new - Tudor Dynasty.