Answer:
Fort Sumter in Charleston, South Carolina was one of the four forts that had not yet been captured by the Confederates, so Lincoln wanted to keep the fort at all costs in order to keep the Union's strenght in the South. He sent unarmed ships to supply the fort with military and food supplies. The Confederate President Jefferson Davis gave command to Southern forces led by General Beauregard to bomb the fort on April 12 to force it to surrender, which happened.
The Northern states all supported Lincoln. He called for the fortresses to be reclaimed and the Union to be preserved. At the same time, 75,000 volunteers were called up for a period of 90 days. In the previous months, several governors had trained their militias. Their troops started to move the next day.
