In the rugged and remote region of Waziristan on British India's northwest border with Afghanistan, mountain tribes of Muslim fighters rebelled against the British Indian Army in numerous operations. The Waziristan Revolt of 1919–1920 was sparked by the Afghan invasion of British India in 1919. Though the British made peace with the Afghans, the Waziri and Mahsud tribesmen gave the imperial (almost entirely Indian) forces a very difficult fight. Some of the tribesmen were veterans of the British-organised local militias that were irregular elements of the British Indian Army, and used some modern Lee–Enfield rifles against the British Indian forces sent into Waziristan. One aspect of this conflict was the effective use of air power against the Waziris and Mahsuds. This is similar to Royal Air Force tactics in suppressing the Arab Revolt in Iraq in 1920 and 1921.