Final answer:
Princess Margaret couldn't marry Peter Townsend due to his divorcee status and the restrictions on remarriage within the British royal family and the Church of England.
Step-by-step explanation:
Princess Margaret was unable to marry Peter Townsend due to several reasons. Firstly, at the time, Townsend was a divorcee, and remarriage to a divorced person was generally frowned upon in the British royal family. Additionally, Margaret was the sister of Queen Elizabeth II, who was the head of the Church of England. The Church of England did not allow divorcees to remarry if their former spouse was still alive. As a result, marrying Townsend would have caused a major controversy within the Church and the royal family.