How was Columbian exchange significant to world history

Why was the monroe doctrine necessary?

What was the main point of helen hunt jackson's book, century of dishonor? a.it showed how unfairly american settlers were treated by the us government. b.it proved that american government was not responsive to the will of the people. c.it made the point that free land was no longer available to new settlers out west. d.it outlined the poor treatment of the native americans by the government.

The constitution did not mention corporations in article i, section 10, so how did justice marshall justify ruling that dartmouth's charter was a contract?