He makes this point on Abraham Lincoln's election, "Lincoln’s election was in part the result of divisions among Democrats. Lincoln’s opposition to slavery was laudable. However, to him it was far less a humanitarian concern than a smart position in the political power struggle between the North and the South over representation and taxation."
While this is a point that involves judgment and not just factual occurrences, it's wrong. Lincoln was seriously opposed to slavery, seeing it as a moral evil and a threat to democracy in the US. He shared the white supremacist assumptions of most of his fellow white Americans and emphatically denied prior to the war that he wanted social equality for blacks. Although he did insist on civil equality before the law.
He describes the Republican Party's Southern Strategy identified with Richard Nixon and connects it to the situation prior to the Civil War that gave Southern states disproportionate power over the national government through the 3/5 clause of the Constitution, "The industrial and industrious Northeast and Western coastal states are politically underrepresented and fiscally exploited by a conservative, backwards and economically weak South."
That strikes me as more of a metaphor than substantive connection, but it's an interesting one. He makes the point by emphasizing the structure of the US Senate, in which each state has two Senators regardless of population:
... the Senate is even more dysfunctional today as it was back then because many more small states were added after 1861.This is true. But it's not different from what it was prior to Civil War. The 3/5 Compromise in the Constitution gave the slave states a "slave bonus" in the allocation of the number of seats in the House of Representatives, because 3/5 of slaves were counted as part of the state's population for allocation purposes but none of those slaves could vote.
As a result, large states (and the vast majority of Americans) are effectively tyrannized by the increasingly extremist majority of Republican senators representing small states.
Two senators serve the population of 574,000 souls in the state of Wyoming, while the same number of senators serve 40 million people in California.
In fact, if you look at senatorial races in 2016, 2014, and 2012 combined – a period during which all 100 seats of the U.S. Senate were up for election – Democrats received more than 10 million more votes in all senatorial races than Republicans. In a proportionate voting system, this would lead to a current Democratic majority of 54-46, rather than the Republican majority of 51-49.
He goes on to describe the effects of gerrymandering that does give Republicans an unfair advantage today in the House. And he also describes a similar effect in the Electoral College in selecting a President.
Those are important points. But in his introductory paragraph, it frames it, "It is easy to date the “official” American Civil War. It occurred between 1861 and 1865. It is far more complex to answer the question whether the Battle of Appomattox truly resolved what so deeply divided the United States of America back then." And his essay looks at that problem in the context of the structural issues of how the Constitution sets up the federal government.
But the issue that produced a Civil War in the context of those structural issues was slavery. And that issue was settled by the Civil War.