The dynasty replaced the Qajar dynasty in 1925 after the 1921 coup d’état, beginning on 14 January 1921 when 42-year-old soldier Reza Khan was promoted by British General Edmund Ironside to lead the British-run Persian Cossack Brigade. About a month later, under British direction, Reza Khan’s 3,000-4,000 strong detachment of the Cossack Brigade reached capital in what became known as the 1921 Persian coup d’état.