Final answer:
Option (b), The War of 1812 led to the reaffirmation of American independence and a shift toward adopting Federalist policies like a national bank and protective tariffs, ultimately fostering national unity and the Era of Good Feelings.
Step-by-step explanation:
An effect of the War of 1812 was that it reaffirmed American independence and caused a shift in attitudes towards national policies. The war revealed the shortcomings of Jeffersonian Republicanism in terms of military preparedness and economic autonomy.
President Madison, who initially opposed the idea of a national bank, realized the value in some Federalist policies such as having a national bank, and protective tariffs, and embraced the idea of a standing professional army and navy. These events helped pivot the nation towards the Era of Good Feelings and signified the end of the old Federalist Party as the Hartford Convention discredited their image.
The War of 1812 led to significant changes in American self-perception and policy, marking a transition to embracing more national institutions in line with Federalist ideas while maintaining Republican ideals. The war helped create a new economy that was less dependent on international trade and more focused on domestic manufacturing and industry, exemplified by the Market Revolution and the growth of the American industrial sector.