Then let me take a crack at it.
Without notifying Congress, Lincoln sent a fleet of Union warships under command of a retired junior Naval officer under orders to send supplies to a group of Union soldiers that were about to surrender...
Leaving aside for the moment that Congress was in recess, why would Lincoln have been required to obtain the approval of Congress to exercise his powers as commander-in-chief?
... and leave a fort with no function other than to force taxation of the local people.
Sumter was built to protect Charleston from attack by a foreign power. You can say that the troops were there to protect Charleston. You can say the troops were there because Lincoln wanted to make a point and show he did not recognize that the southern acts of secession were legal. But please don't resort to that patently false crap that the fort was there "to force taxation of the people." That was never it's purpose.
Their resistance became labeled rebellion, despite the absence of any other higher authority from which to rebel, except a sitting U.S. president who had vowed to protect the revenue stream from Southern production.
Their actions were a rebellion in any sense of the word. An unsuccessful rebellion as it turns out.
Lincoln picked the timing, and it appears he did so deliberately to avoid any issues with Congress telling him "no."
If you are going to deliberately start a war, best to do it when Congress cannot stop you.
Their actions were a rebellion in any sense of the word.
Not for a nation that was founded on the premises articulated in the Declaration of Independence. You may not have noticed, but Independence was listed as a right of man, therefore it was rebellion to oppose what they did.
Lincoln rebelled against the principles founded in that document "four score and seven years" earlier.
Also, "rebellion" is what servants do to masters. If England leaves the EU, it's not "rebellion", it's a peer state leaving a collection of other peer states.