Why did Henry VII and Elizabeth of York have a long engagement after Henry conquered England? He could marry her very quickly but he didn't.
If my memory serves me well, there was the five month gap between Henry VII’s victory at Bosworth Field and his wedding to Elizabeth of York.
On 15th September 1485, writs were issued for Henry VII’s first parliament to be held on 7th November; at the same time, Elizabeth was living with Lady Margaret Beaufort, Henry’s mother. Henry’s coronation followed shortly after the battle of Bosworth and his triumphal arrival in London – on 30th October 1485, a week before the assembly of his first parliament.
Henry couldn’t marry Elizabeth when she was still considered illegitimate. So the first thing he had to deal with was the legitimization of Edward IV and Elizabeth Woodville’s children and the cancellation of Titulus Regius, the pivotal act passed by Richard III that declared Edward IV’s marriage to Elizabeth Woodville null and void on the grounds of his secret pre-contract to Lady Eleanor Butler (I don’t believe that this pre-contract existed). Henry’s first parliament repealed Titulus Regius. At the same time, Henry and Elizabeth were already communicating, trying to get to know each other better.
There was another important thing – they needed to procure a papal dispensation to go ahead with the marriage. Elizabeth and Henry were related by blood: they were distant cousins as they both descended from John of Gaunt. So they needed a dispensation, and it took some time to get it. Once they received it, they were officially married on 18th January 1486, in Westminster Abbey. If they consummated their relationship before the exchange of marriage vows, Elizabeth could have already been pregnant at that time of their public marriage.
Actually, Henry VII didn’t have much time to revel in the laurels of his victory. He had much work to do in England after Richard III’s defeat: peace had to be established, he wanted to be crowned before marrying Elizabeth, and he had to eliminate the obstacles to his marriage, making sure that his union Edward IV’s eldest daughter would be indisputable. He couldn’t marry her immediately after his victory, and so Elizabeth had to wait for several months; I think she enjoyed the moment of quietude after the two uncertain and unhappy years of her life during the reign of her uncle Richard.
There is one interesting post explaining why Elizabeth of York, who had a stronger blood claim to the throne of England, would have never been accepted as a queen regnant. If you wish, you may check it. The link is here.