Answer:
From 3100 BC to 400 BC Ancient Egypt was a successful center of civilization.
Explanation:
Ancient Egypt was a civilization that developed along the middle and lower reaches of the Nile from about 3150 BC until it was conquered by Alexander the Great in 332 BC. It extended south from the Nile estuary to Jebel Barkal near the fourth cataract.
Egyptian civilization depended on the River Nile. When the rains further south caused the river to overtop its banks and cover much of the land, it would immediately irrigate and fertilize the land. This was of great importance in a country where there is virtually no rain.
There was a large desire for slaves because these slaves didn't need to be paid, as long as they were fed, they would be able to work for any amount of time for next to no cost at all.
I believe the answer is Barbed Wire.
Befor the inventions of barbed wire, the Cattles are let to roam freely across the plains and the owners are required to pay a lot of cowboys to supervise them so they didn't go missing. Witht he invention of barbed wire, they can keep the cattle in a secure place without supervision.
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