 Complete the following phrase:  Occupied by Spain until 1975, Western Sahara has been on the United Nations list of non-self-governing territories since 1963 after a Moroccan demand. It is the most populous territory on that list, and by far the largest in area. In 1965, the United Nations General Assembly adopted its first resolution on Western Sahara, asking Spain to decolonize the territory. One year later, a new resolution was passed by the General Assembly requesting that a referendum be held by Spain on self-determination. In 1975, Spain relinquished the administrative control of the territory to a joint administration by Morocco which had formally claimed the territory since 1957 and Mauritania. 