Why are the real income levels of americans so much higher today than they were 100 years ago?

How did the war of 1812 contribute to an increase in u.s. manufacturing? a) the war provided more resources for factories to increase production. b) the war promoted trade between countries so that americans could focus on fighting. c) the war cut americans off from their previous supply of imported manufactured goods. d) the war limited transportation in america, making it necessary to import manufactured goods.