Complex sentence: The result was an unexpected landslide victory for Clement Attlee's Labour Party, over Winston Churchill's Conservatives, the first time the party had lost the popular vote in a general election since the 1906 election; they would not win it again until 1955.
Split into simpler sentences: The result was an unexpected landslide victory for Clement Attlee's Labour Party, over Winston Churchill's Conservatives. It was the first time the Conservatives had lost the popular vote since the 1906 election; they would not win it again until 1955.