A: The Civil War Assuming that you're talking about the American (U.S) civil war, that is.
The civil war was a conflict between the rights of the (slave owning) states and the national government. A war about state rights.
The war of 1812 was between 2 independent, sovereign nations. The great depression was just an economic thing. The northwest ordnance, I have the least knowledge of, but it still wasn't between states and the national government. Hope this helps.
The Civil War was the most dramatic example of conflict between state and national governments. In this war, Southern states followed their perceived right to leave the national government and form a new country.
