This begs the question if Lincoln broke the Constitution. It's a "have you stopped beating your wife" type of question. There are two sides to the question, but I am of the opinion that the President did not exceed his authority, and that it was the Southern States that were acting unconstitutionally by attempting secession by force of arms.
If the South had wanted to test the Constitutionality of secession, they should have done so through the Supreme Court, not armed rebellion. By raising an army, they violated Article 1, Sections 8 & 10, and allowed habeas corpus to be suspended under Section 9.
So, instead, the matter was resolved by force of arms; the questions of secession and the keeping of slaves was a fait accompli, and the Southern cause was lost.
You pays yer money, and you takes yer chances.
Ironically, you state Lincoln didn't overstep the bounds of the USC, but you admit the suspension of the habeas corpus, incorrectly placing blame on the southern confederacy. Let me remind you the Congress of the CSA voted twice to suspend, and failed to grant approval with Davis' final request. The difference? Congress was called to a vote.
Don't be fooled into thinking it was an emergency and Congress could not be called to session; the WBTS did not happen overnight.
Can you include that specific line items from the Articles and dates where they were violated (incl. by whom)?