Why did Henry VII need to reassert his authority over the nobility, and how did he do it?

Henry VII's reign marked the end of the Wars of the Roses, where king had deposed king as the royal houses of York and Lancaster each claimed they were the true rulers of England. This fighting over the crown had lowered the status of the monarchy, and, in the turmoil, allowed nobles to take the law into their own hands, acting like kings in their own localities. Henry VII therefore had to tame the nobles and ensure they once again answered loyally to the King, and ensure that the Crown was more powerful than any of its powerful subjects. Henry did this in four basic ways. 1: He reduced the number of nobles. Every 25 years, 25% of noble families died out. So Henry just stopped making more. Rather than giving out titles and land, he appointed 37 people to the Order of the Garter, which gave them no land or power. Because the nobility then got smaller, it became easier to control. It also meant he got richer, by absorbing the lands from noble families which had died out. 2: He kept surveillance on the nobility, with spies. He prevented powerful families from marrying each other, so they wouldn't create a power block wealthy enough to challenge him. 3: He threatened them financially to ensure their loyalty. He frequently used bonds and recognisances, which were basically agreements that if the nobility breached certain conditions, they would have to pay him money. The Marquess of Dorset, for instance, had to agree that she would pay £100,000 to Henry if she didn't show 'good behaviour'. Out of 62 nobile families, Henry held 46 under some kind of financial threat. 4: He acted against retaining. Retaining was when a nobleman kept men in their service, which was necessary for the basic running of the household, but could be abused and used to raise up an army against the King. Henry passed 2 laws, in 1487 and 1504, that meant you now had to have a license to retain men, and fined you £5 for every person you illegally retained. Henry ruthlessly applied this - he even fined his own mother. Combined, these methods meant that Henry was, without doubt, the most powerful man in the country. If any nobles wanted to oppose him, they would find it far harder to.