Your question is itself unworkable for any one cause as the war it irreducably complex. Combination of causes...well, according to my own beliefs, the following roughly sums up what I think to have brought about the conflict.
1. The majority of your average confederate citizens likely took a side-with-the-homeland approach in secession and a defend-the-homeland approach in war.
2. Any persons involved in the economic activities of industrial manufacturing or agricultural production was inclined to side with one or the other for economic policy reasons. Public choice dictates that they act out of their best interests, inclining industrialists to seek protection for their industries and agriculturalists to seek free trade for their commodities. This is where the issue of the tariff and trade comes into play.
3. Persons with an economic intvestment in slaves sought the liberty to employ that investment in the territories to their benefit, whereas persons uninvested in slaves were economically motivated to oppose it due to the competition in labor slavery provided when along side free workers. Moral arguments bolstered this position, but tended to be in far smaller numbers than is often suggested.
4. An ideological battle existed on the proper role of the national government and its interaction with the states - what right did Congress have to interfere with a state's government or ensure that state's obediance to a federal policy. Constitutional arguments about the system of government and secession as a legal argument fit in here.
5. Political factions were self-interested in preserving/achieving majorities in congress for themselves. Much of the balance depended upon how many new states each region could claim as one of its own during the admittance and expansion of territories. This was a second motivation in the territorial dispute, as it could determine control of the senate.
6. Personal conflicts and emotion entered into the situation among political leaders. Persons of each side found reconciliation or compromise with the other impossible due largely to the hostility between the two, among other things. This exacerbated an already divided situation.
That's probably a fairly accurate, albeit simplified, explanation of my view of the war and its causes - at least covering the big points.
but what real and substantial improvement can you make on McPherson's short sketch?
Noting the factual error of his statements when he dismisses issues such as tariffs and economic disputes as inconsequential or non-regional.