Complex sentence: The British government responded to this near escape by sweeping up much of the United Irish leadership and imposed martial law from 2 March 1797 in an attempt to break the movement by the widespread use of terror during searches for weapons.
Split into simpler sentences: The British government responded to the threat it represented by sweeping up much of the United Irish leadership. It imposed martial law from 2 March 1797 in an attempt to break the movement by the widespread use of terror during searches for weapons.