What issues and ideas promoted sectional conflict during the era from 1815 to 1828?
The era immediately after the War of 1812, which ended in 1815, was marked by an absence of conflict and was known as the "Era of Good Feelings." After the war, the Federalists, who had opposed the war, largely collapsed, leading to the ascendancy of the Democratic-Republicans (called the Republicans) under Monroe and a period of economic nationalism.
However, sectional conflicts developed during the Missouri Compromise of 1820, in which Maine (carved out of Massachusetts) became a free state and Missouri a slave state in order to keep a precarious balance between slave and free states (in addition, the parallel of 36°30′ was marked as the division between slave states to the south and free states to the north). During the presidency of John Quincy Adams (1825-1829), a Democratic-Republican, a philosophy that was opposed to the Republicans began to take shape. In fact, after serving as President, John Quincy Adams became a National-Republican and later a Whig. He believed in many of the pillars of what would become the foundation of the Whig party, including a high tariff and internal improvements such as road and canal building (these were referred to as "the American System.")
Later, as more states came into the union and as the National-Republicans opposed the policies of Andrew Jackson, a Democrat who followed John Quincy Adams as President in 1829, sectional conflicts became more intense. The conflicts centered around abolitionism and whether new states should be free or slave; in addition, the Whigs favored industrialization, while the Democrats favored agrarianism.