Final answer:
The best explanation for how the War of 1812 affected the United States is that it led to a rise of nationalism as Americans rallied together and emerged with a strong sense of national identity after defending against the British. The correct option is d).
Step-by-step explanation:
The War of 1812 had a significant impact on the United States. It did not lead to a decline in isolationism or nationalism, nor did it result in an immediate shift in American relationships with Canada or the Native Americans. Instead, the primary effect of the War of 1812 was a substantial increase in nationalism within the United States.
This surge in national pride stemmed from Americans having successfully defended their country against an external threat, the British, and it helped forge a stronger common identity across the nation.
The war also marked the end of the Federalist Party due to its association with anti-war and secession sentiment at the Hartford Convention, and it gave a start to the political career of the formidable Andrew Jackson.
Furthermore, it also paved the way for westward expansion, as Native American resistance in the Northwest was significantly weakened.
Based on this information, the statement that best explains how the War of 1812 affected the United States is: d) It led to a rise of nationalism as Americans developed a common identity and fought off an enemy.