The Organization of Islamic Cooperation (OIC) is the second-largest inter-governmental organization after the United Nations, comprising 57 member states. Its establishment was a direct response to the arson attack on the Al-Aqsa Mosque in Jerusalem in August 1969, which deeply outraged the Muslim world. Following this incident, leaders of Islamic nations convened a historic summit in Rabat, Morocco, from September 22-25, 1969. This summit led to the formal establishment of the OIC, with the primary aim of fostering Islamic solidarity and cooperation among member states.
Therefore, September 1969 is the correct answer. The other options, May 1970, May 1971, and September 1972, are incorrect. While the OIC held subsequent meetings and adopted its charter in later years, the foundational act of its establishment occurred in September 1969. These later dates might correspond to other significant events in the OIC's early history, but not its initial formation.