from what I understand about the civil war time, that it was started at Harpers Ferry, WV, and the Pres at the time sent in the Marines to quill an unrest that was going on there.
At the same time the southern state were talking about secession from the Union.
Harpers Ferry was also where the US Gov, was having all it's guns made.
Please forgive my nit picking but the first shot was fired at Fort Sumter, SC when a Confederate battery fired upon the fort to attempt to stop the resupply of the fort which was, at the time, under seige by the Confederate forces in an effort to force the Union troops out of Charleston Harbor and to free up the port for Confederate use.
Harpers Ferry was indeed a Federal Armory but not the site of the start of the "War of Northern Aggression". (See = John Brown's attack on Harpers Ferry.)
edit to correct spelling of course
seige - siege - whatever - the "blue bellies" were surrounded