Archaeological explorations in Angola have been carried out since the late 19th century. Much of the early research was funded and led by Portuguese colonial interests in Angola, fueled by the Scramble for Africa. The 1890 British Ultimatum on the expansion of the Portuguese Empire led to the latter's further emphasis on colonial development in central Africa, including Angola, and the exploration of its cultural resources to strengthen its colonial system. In the 20th century, archaeology in Angola focused largely on the Stone Age, driven by colonial interests in evolutionary anthropology, until Angolan independence in 1975. During that time, several research institutions and museums were opened, and fieldwork was largely tied to mission trips into the country to document the cultures of native Angolans. In recent decades, partnerships have formed between Angolan archaeologists and those from France and Portugal to continue research. Calls to repatriate artifacts back to Angola from overseas collections have also gained momentum in recent decades.