Complex sentence: The areas' existence was a challenge to the authority of the British government in Northern Ireland, and the army finally demolished the barricades and re-established control over the areas in Operation Motorman on 31 July 1972.
Split into simpler sentences: The areas' existence was a challenge to the authority of the British government in Northern Ireland. The British army demolished the barricades and re-established control in Operation Motorman on 31 July 1972.