Assumed they had clean energy,
Lupe is saying that the archaeologists assumed that the civilization had clean energy because they were so advanced technologically (renewable resources) and were probably educated and concerned about the environment.
Instead of spending trillions of dollars on foreign wars the United States could be investing in increasing renewable energy sources (such as solar, wind power and wave power) and reducing dependence on non renewable resources (petroleum, natural gas, coal). This could both reduce conflict with other nations as well as creating jobs in America.
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