Since 1944, Iran was a constitutional monarchy ruled by the Shah Mohammad Reza Pahlavi. From the discovery of oil in Iran in the late nineteenth century major powers exploited the weakness of the Iranian government to obtain concessions that many believed failed to give Iran a fair share of the profits. During World War II, the UK, the USSR and the US all became involved in Iranian affairs, including the joint Anglo-Soviet invasion of Iran in 1941. Iranian officials began to notice that British taxes were increasing while royalties to Iran declined. By 1948, Britain received substantially more revenue from the Anglo-Iranian Oil Company (AIOC) than Iran. Negotiations to meet this and other Iranian concerns exacerbated rather than eased tensions.