Time Line:
March 4th Lincolns Inaguration
April 12th Sumpter
April 15th Lincolns call for troops to invade Virginia
April 17th Virginia's secession
April 18th Virginia takes Harpers Ferry
July 25th Congress Finally declares war
So it is Mr Lincolns War
That timeline neglects events that followed the secession of 7 states (starting with South Carolina on December 20, 1860), and before Lincoln was inaugurated as President of the United States on March 4, 1861. Those events include the belligerent acts of State authorities taking unlawful possession of federal installations including arsenals, forts, and custom houses.
Two examples are:
1. US Arsenal and Barracks in Baton Rouge, Louisiana. In January 1861, Louisiana Militia and the Washington Artillery presented an ultimatum to the commander of the facility, Captain Joseph Haskin:
"The safety of the State of Louisiana demands that I take possession of all Government property within her limits. You are, therefore, summoned hereby to deliver up the barracks, arsenal, and public property now under your command. With the large force at my disposal this demand will be enforced. Any attempt at defense on your part will be a rash sacrifice of life."
2. General David Twiggs surrendered his command, which included all federal installations, property, and soldiers in Texas to the Confederacy in February 1861. For this act, Twiggs was dismissed from the US Army on March 1, 1861 for "treachery to the flag of his country."
In its final months, the Buchanan administration did little to resist these and other aggressive acts beyond instructing its officers to "protect government property." It would take Lincoln to assert, on becoming President that "The power confided to me will be used to hold, occupy, and possess the property and places belonging to the Government and to collect the duties and imposts." If that Constitutional vow is considered to be the reason for "Lincoln's War" so be it.