Jackson Conspiracy

King Andrew was called so due to his abuse of power. Above abusing power, he also wanted to extend the powers of a President. The Whig party feared that his increased power would lead to a king-like rule, thwarting all they had done to win independence. Andrew Jackson continued his plans with the expulsion of the Indians, despite Congress' intrusion on the plans, declaring it "unconstiontitutonal". This defiance of Congress built on his "king" title. His prejudice against banks was a fault, as well. The absorption of power from the National Bank made Jackson appear as if he was taking the power in exchange. More power, means more king like.
The nullification crisis also created a King like essence to Jackson. The dislike for tariffs or imported goods was enough for the South to even try to make themselves separate from the United States as a whole. Taxes always related back to a "king", such as during the American Revolution. Considering, the King's taxes are what brought Americans overboard at that time, it was a great blow to what the South demanded. Though there was taxation with representation, the South would not settle for such terms, and deemed Andrew Jackson as King Andrew.

Coexistence?

"How could both Sectionalism and Nationalism exist at the same time and at the same place?"

Sectionalism and Nationalism can coexsist in the same place just like how an Arabic person can reside in the States.
Everyone is "yaay for equal rights!", yet people demand that someone wearing a turban in the airport should be throughly checked for explosives.

They are contradicting terms, yet they were team players during The Era of Good Times.
While the south encouraged the use of slavery so that its economy could still thrive, other states began to become "free states". which spurred the south's need to become sectionalist. If they could diverse themselves from the rest of the country, they could continue to have slave labor.

Despite wanting to have slaves, the south also wanted to be involved in nationalism. The wanted the benefits of having a government not impaired by other world powers.
This sense of nationalism increased after the War of 1812. The sense of being an American enforced the want of nationalism.