Final answer:
The first event was the Passage of the Missouri Compromise in 1820, preceding other significant events such as the Compromise of 1850, Kansas-Nebraska Act, publication of "Uncle Tom's Cabin," the Lincoln-Douglas debates, and the formation of the Confederate States of America.
Step-by-step explanation:
The event that happened first among the options provided is the Passage of the Missouri Compromise. The Missouri Compromise was passed in 1820, well before the other events listed. It was an important piece of legislation aimed at maintaining the balance of power between slave and free states. The Compromise allowed for the admission of Missouri as a slave state and Maine as a free state, while also establishing a line (36°30' parallel north) across the former Louisiana Territory, north of which slavery was to be prohibited.
Following the Missouri Compromise, the Passage of the Compromise of 1850 attempted to address the issue of slavery once again by admitting California as a free state and enacting the Fugitive Slave Act, among other provisions. Later, the Passage of the Kansas-Nebraska Act in 1854 overturned the Missouri Compromise by allowing these territories to decide the issue of slavery by popular sovereignty. Publication of "Uncle Tom's Cabin" occurred in 1852, influencing public opinion on the issue of slavery. The Lincoln-Douglas debates took place in 1858 as part of the Illinois Senate race, which set the stage for Abraham Lincoln's presidential campaign. Lastly, the Formation of the Confederate States of America took place after Lincoln's election in 1860, prior to his inauguration in 1861.