 Following the 1979 Islamic Revolution, Iran and Saudi Arabia (considered the "leading state authority" of Shi'a and Sunni Muslims, respectively) began to use Pakistan as a battleground for their proxy sectarian war, and Pakistan's support for the Deobandi Taliban organization in Afghanistan by the 1990s became a problem for Shi'a Iran, which opposed a Taliban-controlled Afghanistan.Nevertheless, both countries continue to cooperate economically where possible and are forming alliances in a number of areas of mutual interest, such as fighting the drug trade along their border and combating the insurgency in the Balochistan region.Iran has also expressed an interest in joining the China–Pakistan Economic Corridor (CPEC).