Complex sentence: The letters patent issued by Edward III limited the right of succession to male heirs, which placed Richard's uncle John of Gaunt, Duke of Lancaster, and his male descendants ahead of Philippa's male children in the succession.
Split into simpler sentences: The letters patent issued by Edward III limited the right of succession to male heirs. This meant that John of Gaunt, Duke of Lancaster, and his male descendants were placed ahead of Philippa's male children in the succession.