Complex sentence: The district and its antecedent have been favorable to electing Progressive Conservative candidates in the past few decades, but this history was broken in the Alberta general election, 2012 when Wildrose candidate Pat Stier was elected.
Split into simpler sentences: The district and its antecedent have been favorable to electing Progressive Conservative candidates in the past few decades. But in the Alberta general election, 2012 Wildrose candidate Pat Stier was elected.