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Ghana

Explanation:

was a West African empire located in the area of present-day southeastern Mauritania and western Mali. Complex societies based on trans-Saharan trade in salt and gold had existed in the region since ancient times,[1] but the introduction of the camel to the western Sahara in the 3rd century CE, opened the way to great changes in the area that became the Ghana Empire. By the time of the Muslim conquest of North Africa in the 7th century the camel had changed the ancient, more irregular trade routes into a trade network running from Morocco to the Niger River. The Ghana Empire grew rich from this increased trans-Saharan trade in gold and salt, allowing for larger urban centres to develop. The traffic furthermore encouraged territorial expansion to gain control over the different trade routes.

4 copper and gold, the california gold rush is why im pretty sure.

increase in population