What was a cause of the Mexican-American War?

What is the name for the main idea behind the settling of western lands by americans in the early-1800s?

The economy shifted from to industrial during the first industrial revolution

How did the construction of the erie canal improve transportation in the united states in the 1820s? a. the canal connected the great lakes to the mississippi river. b. the canal connected the great lakes to the ohio river. c. the canal connected the atlantic and pacific oceans. d. the canal connected the great lakes to the atlantic ocean.