Complex sentence: By the end of the 1920s, the Labour Party had replaced the Liberals as the Tories' main rival and the party went into decline and by the 1950s won no more than six seats at general elections.
Split into simpler sentences: By the end of the 1920s, the Labour Party had replaced the Liberals as the Tories' main rival. The party went into decline and by the 1950s won no more than six seats at general elections.