<Tr> <Td_colspan="3"> Area </Td> </Tr> <Tr> <Td> </Td> <Td> 1500 </Td> <Td> 1,400,000 km (540,000 sq mi) </Td> </Tr> <Tr> <Td> </Td> <Td> 1550 </Td> <Td> 800,000 km (310,000 sq mi) </Td> </Tr> <Tr> <Td_colspan="2"> Currency </Td> <Td> (Cowry shells, and gold coins) </Td> </Tr>

What caused the decline of ghana mali and songhai