[Non-Sequitur]

Last I checked, that "force" was only intended to remove a hostile nation's troops from within the confederate's own border.

The hostile 'nation' in the picture was the confederacy. The Union soldiers were in a fort that was the property of the United States and no hostile actions on any kind had been made before the confederacy decided to shell the fort.

[GOPcapitalist]

The hostile 'nation' in the picture was the confederacy. The Union soldiers were in a fort that was the property of the United States

The yankees had no legitimate right to be there. Their presence itself initiated the hostilities.

and no hostile actions on any kind had been made before the confederacy decided to shell the fort.

Not true. The yankees fired on a confederate ship entering Charleston harbor the day before Beauregard ordered the shelling commenced.