The Southern Confederacy next invaded Manassas (21 July 1861) forty miles west of Washington. (1st. battle of Bull Run) - therefore the South was the agressor in that it invaded the North,it became a war between the states; The Union vs The Confederacy who wanted to secede from the Union.
So I suggest you call the war the proper name "The War Of Secession". Or maybe to reverse the South's name - the Union called it "The War Of Southern Rebellion" or in your term "The war Of Southern Agression".
You are forgetting that the north did everything it could to provoke the southerners into war. Lincoln was quite relieved when the South fired first, because that was always his goal.
Firing on Ft. Sumter, etc. was an act if war. But not just any war. The North was by no means empowered to conquer the Confederacy and reintegrate secessionist stated because they stole federal property. Taking back the forts and demanding retribution and reparations, that’s what Sumter justified, if that. Not total war, unconditional surrender, and occupation which in a sense persists to this day.
As for the notion that the South invaded the North, lol. Who are you kidding? Even if we take your point about Bull Run on its face, that was only after the blockade of Southern ports, which SCOTUS later pinpointed as the start of the war, and Lincoln’s (unconstitutional) call for volunteers, not to defend Washington but obviously to crush the “insurrection.”
act if war = act of war
Check your atlas. Manassas is in Virginia. If the south legally had the right to secede, then moving an army to a town within its own borders could hardly be called an invasion. Further, the fact that Ft Sumter was not evacuated by the Federal troops was a breach of Confederate sovereignity which could legitimately be construed as an act of aggression. Think about the response that the US would have had if the British had failed to evacuate New York, for instance. Would the US have been an aggressor if the British had maintained garrisons in US territory and the US attacked those garrisons?
Obviously, the north had the moral high ground, but it’s quite possible to make a legalistic argument that the north in fact was the aggressor in the civil war.