Complex sentence: In 1891, he entered into politics, winning unopposed the riding his father had held until he died that year, and held that seat in the British House of Commons until he inherited his uncle's dukedom in 1908.
Split into simpler sentences: In 1891, he entered into politics, winning unopposed the riding his father had held until he died that year. He held that seat in the British House of Commons until he inherited his uncle's dukedom in 1908.