[FR_addict]

Lincoln sent a fleet of warships to Ft. Sumter in South Carolina. Sending military war ships after the North agreed to withdraw the garrison was tantamount to a declaration of war.

In his inaugural address, he said he had no intention of declaring war over the slavery issue, but that the peservation of the union would force his hand.

His inaugural address is before the beginning of the Civil War. I'll take Lincoln at his own words as to what he considered important enough to cause him to take military action and that is the secession of the states:

1) Slavery
"I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so... "

2) prevent competent resident citizens from holding the Federal offices (secession means that no one would hold Federal office)

"unless it be forced upon the national authority. 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; but beyond what may be necessary for these objects, there will be no invasion, no using of force against or among the people anywhere. Where hostility to the United States in any interior locality shall be so great and universal as to prevent competent resident citizens from holding the Federal offices, there will be no attempt to force obnoxious strangers among the people for that object."