Final answer:
Option (c), Between 1791 and 1821, the United States admitted several new states including Indiana and Mississippi in 1816 and 1817 respectively, as well as Illinois, and Alabama in 1818 and 1819.
Step-by-step explanation:
Between 1791 and 1821, the new states admitted to the United States included both Kentucky and Tennessee as well as Ohio, Indiana, Mississippi, Illinois, Alabama, and others. Specifically, during the period of 1816 to 1821, the states of Indiana (1816), Mississippi (1817), Illinois (1818), Alabama (1819), Maine (1820), and Missouri (1821) were admitted to the Union, reflecting a complex period of growth and regional tensions particularly related to the expansion of slavery.
The expansion of the nation and the new states entering the Union were impacted by the emerging sectional differences that were partly represented by the contrasts along the Ohio River Valley, with slave states like Kentucky and Tennessee to the south and free states like Ohio, Indiana, and Illinois to the north. These admissions reflect the growing infrastructure needs and the sectional debates that would eventually lead to the Civil War.