His first rising failed in 1483, and then in 1485 he tried again in the form of the battle of Bosworth. Henry won the battle and was crowned Henry VII. Henry's success at Bosworth was greatly helped by Lord Stanley, without whom Henry would almost certainly have lost and Richard III would have remained king. This victory at Bosworth helped secure the throne for Henry.
Once Henry was on the throne, it was a tough job for him to keep it. Henry deliberately arranged for his coronation to take place before the first parliament. This is because although he was officially king, it could never be said that parliament made Henry king. He also intended to marry Elizabeth of York, thus finally uniting the two houses of York and Lancaster, but also to further strengthen and justify Henry's claim on the throne. As Henry and Elizabeth were distant cousins it was necessary to apply for papal dispensation, the inevitable delay ensured that no one could say that Henry owed his crown to his wife. When Henry became king he dated the official start of his reign before the battle of Bosworth. He could therefore call Richard's supporters in the battle traitors have then executed for treason.
Before Henry had been on the throne for one whole year there were minor risings. Although now we can see that they are fairly unimportant and not really a threat, it was worrying for Henry at the time as he could not tell if the yorkists would support them or not. The risings started when Henry was travelling north to York to establish his presence as king, and secure their support. As Henry travelled north three lords (Lord Lovel and brothers Lord Thomas Stafford and Lord Humphrey Stafford) broke sanctuary. Lovel travelled north to waylay the king; meanwhile the Stafford's went to stir a rebellion in the west. Henry was aware of this, but in order to show his confidence as king and act like he was not worried he continued to York and sent an armed force to the rebels.