C, because that was basically one of the reasons for the Civil War as well. The Northern and Southern states were always fighting about whether slavery should expand west or not.
I would say either B or D but I think the better answer would be D.
Members of the same country (the Confederacy wasn't recognized - it doesn't count as a separate country) were making absolute war on one another. It was brother fighting brother.
We know this by dating the structures, evidence of life there long before anywhere else and by the Bible. You can also look into other sources of history too. There is a ton of info on Egypt provided by scrolls a old writing on stone tablets.
Don’t touch that link and it’s because of their belief and the strong connection they have to god and the time they put into it.