The secessionist states were attacking federal fortifications before Lincoln was even swarn into office. Just a month after being sworn in the Confederates attacked Fort Sumter.
...every one of which was within their borders. If the country splits, it is only reasonable, not to mention efficient, that its previous posessions of the sort be allocated geographically, or are you one of those people who believes that "belonging to the United States" really means "belonging to New England, New York, New Jersey, and Pennsylvania, regardless of where it may be geographically"?
Just a month after being sworn in the Confederates attacked Fort Sumter.
Only after Lincoln instigated that attack. It is commonly known that the confederates opened fire on the fort, but less known (and for a reason) why they did so when they did. A few days before they fired, Lincoln sent a fleet of warships to Charleston tasked specifically with the purpose of reaching Sumter and using military force to do so in light of the inevitable opposition to their entry into the harbor. The day before the attack, one of those ships in Lincoln's fleet arrived at Charleston and even fired upon a confederate civilian vessle that was entering the harbor. The rest were just over the horizon and expected to arrive at any moment. Aware of this, the confederates gave the orders to open fire and preempt their arrival.