Six:
1. Upper Mississippi
2. Arkanas River
3. Illinois River
4. Missouri River
5. Ohio River.
6. Red River
Radiometric dating should be what they use
In addition to a desire for economic profit, nationalism also served as a reason for colonization. After the French Revolution, European nations had a strong sense of national pride, and felt that in order to prove themselves as a strong world power, they would need to gain control of other countries.
These are what is shared between cultures