Final answer:
John C. Frémont was most successful in the Northern region, winning 11 of the 16 free states. He did not win the key battleground states of Pennsylvania, New Jersey, Indiana, and Illinois. His success indicated the Republican Party's growing strength, despite his overall defeat in the election.
Step-by-step explanation:
In the presidential election of 1856, John C. Frémont was most successful in the northern region, where he won 11 out of the 16 free states. However, there were some key states in that region that he did not win. These included the crucial battleground states of Pennsylvania, New Jersey, Indiana, and Illinois. Democrats in these states, wary of Republican policies that could lead to secession and conflict, opted for James Buchanan, who was viewed as a candidate for the Union.
Despite his loss, Frémont's success in the majority of the northern states showcased the growing strength of the Republican Party. However, his defeat also served as a disappointment, particularly among abolitionists and African Americans, who had hoped for a stronger stance against slavery and an advancement of their rights.