Around 1990. That’s according to a fascinating new paper by the economists Matthew Gentzkow and Jesse M. Shapiro and Microsoft Research’s Matt Taddy. Americans have for decades signaled their political clique with specific terms—as when Southerners refer to the Civil War as the “War of Northern Aggression,” or Northerners call it the “Great Rebellion.” What is different today, the researchers said, is “the magnitude of the differences, the deliberate strategic choices that seem to underlie them, and the expanding role of consultants, focus groups, and polls” to entrench two separate political lexicons within the same polity.

In the paper, they have a simple but specific definition of partisanship: “the ease with which an observer could guess a speaker’s party based solely on the speaker’s choice of words.” This definition of partisanship scarcely changed between 1870 and 1990. For roughly 120 years, the probability of correctly guessing a speaker’s party by listening to a one-minute speech was about 52 to 55 percent, nearly random. But suddenly, in the early 1990s, rhetorical partisanship exploded.

The Rise of Partisan Language in Congress

“The 1994 inflection point in our series coincides precisely with the Republican takeover of Congress led by Newt Gingrich” and his Contract With America, they find. Gingrich’s revolution helped to introduce and/or popularize terms like “tax relief,” which at the time were seen as a distinctly conservative frame, as opposed to “tax cut” (or, more partisan, “tax giveaway”).

But the polarization of language did not stop when Gingrich left Washington. The Contract With America kicked off a neologism arms race, a prolonged attempt by members of both parties to coin catchy new terms for their pet policies, particularly for taxes, immigration, and health care. This neologism burst—defined as words and phrases first popularized after 1980—continued through the end of the 20th century and into the 21st century. Both Republicans and Democrats became more disciplined about defining their agendas in partisan-specific terms and getting other members of their parties to speak the same language.

The Rise of Partisan Neologisms

Another inescapable variable here is the significant shift in media technology. Between 1984 and 1992, the cable industry spent more than $15 billion expanding its infrastructure—the “largest private construction project since World War II”—and the number of cable channels nearly tripled in that decade.

The diversity of media, alone, cannot explain the growing partisanship of language. After all, in the 19th century, there were hundreds of ethnic newspapers in the New York and New Jersey area, alone, serving socialists, conservatives, Jews, Swedes, and Italians. But the cable revolution was different by an order of magnitude: Each channel had the potential to reach tens of millions of cable-subscribing voters.