“No, the Civil War started because secessionists started shooting.”
This is Lincoln’s Proclamation of April 15, 1861 where he calls for 75,000 militia to ‘suppress the combinations’ in the States of South Carolina, Georgia, Alabama, Florida, Mississippi, Louisiana, and Texas. It’s as close as he came to a declaration of war and he gives his reason for doing so.
Oddly enough he never mentions Fort Sumter, secessionists, nor shooting.
He does call on “all loyal citizens to favor, facilitate, and aid this effort to maintain the honor, the integrity, and existence of our national Union, and the perpetuity of popular government”, the theme of restoring the Union that ran through his Presidency and the war.
http://hd.housedivided.dickinson.edu/node/35998
He didn’t have to mention the secessionists’ attack on Ft Sumter, it was huge news, and was the event that made the call-up both possible and necessary. That the attack wasn’t too bright goes without saying — it was a Democratic Party idea.