Illinois is one of the most dependably Democratic states in the nation. It has voted for the party’s presidential candidate in seven — soon to be eight — consecutive elections.

But Illinois hasn’t always been Democratic. In fact, we used to be staunchly Republican. From 1860 to 1928, the Land of Lincoln voted for its namesake's party in 16 out of 18 presidential elections, breaking out of its partisan mold only for Grover Cleveland, who chose Illinois’s Adlai Stevenson as his vice president, and Woodrow Wilson, when Theodore Roosevelt and William Howard Taft split the Republican vote.

It isn't Illinois that changed, but the political parties. In the late 19th and early 20th Centuries, the Republicans were a Northern, progressive party, devoted to such reformist causes as abolition, women’s suffrage, and environmentalism. The Democrats were a rural Southern party, suspicious of federal power and determined to preserve the Jim Crow system of segregation. On a map of the 1908 presidential election, the Red States are in the North, the Blue States in the South and West.

Image: 270 To Win

The best way to understand Illinois’s political behavior is not through partisan alliances, but regional alliances. The Chicago area, which contains most of the state’s voters, is a part of what cultural historians Colin Woodard and David Hackett Fischer call “Yankeedom,” or “Greater New England.” It was colonized by migrants from Vermont, Massachusetts, and Upstate New York (most of the city’s early mayors were born in that part of the country), and has consistently shared that region’s political attitudes. In Lincoln’s day, New England-settled northern Illinois was the most anti-slavery part of the state. Today, it’s the reason that Illinois votes more like a coastal state than most of its Midwestern neighbors.

In the 40 presidential elections since 1860, when New Englanders became the dominant force in Illinois politics, we've voted 34 times with Massachusetts, the most liberal New England state. The only period when Illinois and Massachusetts regularly differed was in the 1960s, ’70s, and ’80s, when the Democrats and Republicans were realigning over the issue of civil rights. Massachusetts moved into the Democratic fold first, voting for Hubert Humphrey, George McGovern, and Jimmy Carter, while Illinois voted for Richard Nixon and Gerald Ford. Since the election of Bill Clinton in 1992, though, the two states have always been in sync, as part of what political scientists call the Sixth Party System, and the rest of us call Red and Blue States.

Now let's look at how Illinois compares with Mississippi, the most conservative state in the region Woodard calls Deep South. It’s a truism of American politics that if Yankeedom votes one way, Deep South will vote the other. Since the Civil War, the two regions have rarely agreed on anything. In those same 40 elections, Illinois has voted with Mississippi only 10 times, mostly during the landslide elections won by Franklin D. Roosevelt, Nixon, and Ronald Reagan, “omnibus” candidates who appealed to all parts of the country.

(On this topic: The Republican argument that “Democrats are the party of slavery” is a misreading of history that ignores the fact that regional alliances are more enduring than partisan alliances. In the 1850s, the Republican Party was founded to advance the values of Yankeedom, and oppose a Democratic Party rooted in the Deep South. One could just as inaccurately argue that “Republicans are the pro-choice party,” since most of the justices who voted for Roe v. Wade were appointed by Eisenhower and Nixon.)

In the Midwest, Michigan, Wisconsin, and Minnesota are also considered part of Yankeedom. Minnesota is the only state to have voted Democratic in every election since 1976. Michigan and Wisconsin defected to Donald Trump in 2016, by less than a percentage point each, but Joe Biden is leading the polls in both states this year.

Could Illinois ever vote Republican for president again? It would only happen in a landslide election, in which a Democratic incumbent is rejected as incompetent (as Jimmy Carter was), or a Democratic challenger is considered unacceptably left-wing (as George McGovern was). The only other scenario is another realignment of the two parties, in which the North again becomes Republican and the South Democratic, but that would be decades away, if it ever happens. As it stands now, Illinois is on the Democratic side, an allegiance which can be traced back to colonists who began arriving here 200 years ago.