In 1791 his opponents advanced on all fronts, with the main British force under Cornwallis taking Bangalore and threatening Seringapatam. Tipu harassed his enemy's supply and communication and embarked on a "scorched earth" policy of denying local resources to the invaders. In this last effort he was successful, as the lack of provisions forced Cornwallis to withdraw to Bangalore rather than attempt a siege of Seringapatam. Following the withdrawal, Tipu sent forces to Coimbatore, which they retook after a lengthy siege.