The second was from the mid-20th century when the discovery of vast oil deposits propelled it into a key economic and geo-political role. At other times, the region existed in relative obscurity and isolation, although from the 7th century the cities of Mecca and Medina had the highest spiritual significance for the Islamic world, Mecca being the destination for the Hajj annual pilgrimage. For much of its history most of the Arabian Peninsula has been controlled by a patchwork of tribal rulers.