This event led to secession of seven southern states.

The correct answer is the Civil War.

Explanation:

https://en.wikipedia.org/wiki/Timeline_of_events_leading_to_the_American_Civil_War

Election of 1860

Explanation:

It was the election of Abraham Lincoln as president which caused the Southern states to secede. Lincoln was elected president on November on November 6, 1860, and secession began just a few weeks later: South Carolina went first, on December 20, followed by Mississippi on January 9, 1861, and then by Florida on the next day.For the Southern states, secession from the Union was about saving slavery.

20 years ago

explanation:

it was certainly a debatable decision, mainly because it was based primarily on political - and not on legal or social - views. since the congress at that time was led by members of the republican party, and the territory that the tribes wanted to turn into an exclusively indian state was predominantly democratic, the proposal (as expressed in the constitution) did not succeed, but the constitution itself proved to be of crucial importance in the creation of the state of oklahoma, and, most importantly, it guaranteed the involvement of representatives of the indian tribes in the government of the future joint state.  

as a member of congress, i would have voted to ratify the constitution, or at least to have it tabled. ignoring it was an interested and partial decision.