The Islamic Republic of Iran also known as Persia, is a country in Western Asia. With 78.4 million inhabitants, Iran is the world's 17th most populous nation. It is also the nation with the largest Shia population. Iran is home to one of the world's oldest civilizations, beginning with the formation of the Proto-Elamite and Elamite kingdom in 3200–2800 BC. The emergence in 1501 of the Safavid dynasty, which promoted Twelver Shia Islam as the official religion, marked one of the most important turning points in Iranian and Muslim history. The Persian Constitutional Revolution of 1906 established the nation's first parliament, which operated within a constitutional monarchy. Following a coup d'état instigated by the U.K. and the U.S. in 1953, Iran gradually became very close allies with the US and the rest of the West, remained secular, but grew increasingly autocratic. Growing dissent against foreign influence and political repression culminated in the 1979 Revolution, which led to the establishment of an Islamic republic on 1 April 1979. A multicultural nation comprising numerous ethnic and linguistic groups, most inhabitants are officially Shia, Iranian rial is the currency, and Persian is the official language.