What was the number of indigenous people that was decimated within a century?

By the close of the Indian Wars in the late 19th century, fewer than 238,000 indigenous people remained, a sharp decline from the estimated 5 million to 15 million living in North America when Columbus arrived in 1492. The reasons for this racial genocide were multi-layered.

2. a land bridge connected asia and north america thousands of years ago.

4. crossing the land bridge would have been simple for the first migrants.

5. people might have crossed a land bridge while hunting animals.

the answer is b: an economic crisis throughout the country.