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Divisions within the US population on social and political issues have increased by 64% since 1988, with almost all this coming after 2008, according to a study tracking polarization from the end of the Reagan era to the dawn of Trump’s second term.

How US polarization surged after 2008

The University of Cambridge’s Political Psychology Lab analyzed opinions on a wide range of issues—from abortion and equality to traditional values—over almost four decades, and found polarization almost flatlined during the nineties and noughties.

However, starting in 2008—the year of the financial crisis, Obama taking office, and the launch of Apple’s App Store and iPhone 3G—divisions across the board steadily rose, research published in the journal Royal Society Open Science shows.

Most of this shift is down to the liberal side of the American public moving in a more progressive direction. Based on issues surveyed, the US left was 31.5% more socially liberal in 2024 compared to 1988, while the US right was only 2.8% more conservative.

The study, which goes up to 2024, shows that this polarization may have begun to level off during Biden’s term, although it remains far higher than in previous decades.

"Our study shows that 2008 was a major turning point for the divisions between left and right on many of the issues that define contemporary US politics," said senior author Dr. Lee de-Wit, who leads Cambridge’s Political Psychology Lab.

"Although sentiment varies by topic, the American public has moved left on many issues during the 21st century. This shift may surprise those familiar with the rightward turn of Republican leaders over the same period, as well as recent US headlines."

"Right‑leaning Americans have remained fairly stable in their positions for the last 35 years, and may feel left behind as half the country has shifted towards an ever more progressive outlook on many issues," said De-Wit.

"Part of the recent success of the US right may be their ability to tap into outgroup animosity for a perceived ‘woke’ left, rather than a firm belief in some of the more extreme right-wing positions adopted by the Republican leadership."

Using algorithms to track opinion shifts

While similar research has relied on people self-identifying as Republican or Democrat, liberal or conservative, the latest study uses machine learning to go beyond such labels.

The Cambridge team used "clustering algorithms" to examine polarization around underlying issues. This technique has previously been used in everything from sorting soundwaves to psychiatric diagnosis.

"There can be various reasons why voters feel they belong in a particular party, from the media they consume to the communities in which they live, even if many of their attitudes don’t fit," said lead author Dr. David Young, from Cambridge’s Department of Psychology.

"Clustering algorithms provide an objective, bottom‑up way to analyze shifts in political opinion beyond the ideologies of national parties and the self-identification of voters."

The study looked at over 35,000 survey responses gathered between 1988 and 2024 for the American National Election Studies, a research project that has been collecting data on US public opinion since 1948.

The data covered core political issues ranging from economics to race and inequality. Abortion and traditional family ties showed some of the biggest changes, as the rise in progressive attitudes widened divisions from a late-1980s consensus, when right-leaning voters were not so uniformly opposed to abortion, for example.

Health insurance and the question of discrimination against African Americans also showed significant shifts in public attitudes, with widening rifts due to movement in both directions—a "true polarization."

At the other end of the spectrum, the gap between left and right has stayed consistently wide over issues of equality. However, the team found statistically significant increases in polarization on every issue.

Party sorting and sharper political identities

Moreover, researchers found that "sorting"—the degree to which people claim to identify with a party or ideology—has jumped significantly since the late eighties.

By 2024, 20% more people in the left‑wing cluster of the population now call themselves Democrats, and 51% more call themselves liberals, than in 1988. While 30% more people in the right‑wing cluster now call themselves Republicans, and 39% more are self-described conservatives, compared to the end of the Reagan era.

"Sorting increases the difference between Democrats and Republicans even when attitudes don’t change much, so it can be hard to gauge what is driving political polarization," said De-Wit.

"Using machine learning, we can see that both are happening. People are sorting themselves more using political labels, alongside a genuine increase in polarization on the core issues."

Dr. David Young said, "In the past, someone with left-wing views on one issue might have held right-wing views on another. That’s rarer now."

"I think this consolidation happens as people pick up clear cues from political elites about what goes together. It makes average positions more extreme, and widens gaps between US citizens."

Why US divides feel especially intense

However, De-Wit argues that polarization in the US can feel much worse than it is. "Political groups have moved further apart in recent years, but these divisions are still fuzzy, and Americans are not split into entirely opposing tribes when it comes to the issues."

Despite shifts in opinion, both left and right-leaning sides of the US population have stayed the same size since 1988, and the range of opinions within each cluster has not become more diverse. Only the distance between the two has increased.

The latest study also shows that the US is different to most countries around the world, which have unequal sizes of left and right clusters.

In the same Royal Society paper, the Cambridge team report global findings, applying the same clustering algorithms to responses from over 173,000 people across 57 countries between 1999 and 2018.

"In developing countries, we typically see a large culturally conservative majority and a culturally liberal minority. In highly developed countries, we tend to see socially liberal majorities, if only by a small margin," said Young.

"The United States is unusual in having a left and a right of roughly equal size. This has been the case for a long time, and it may help explain why polarization in the US feels so intense."

Unlike in the US, the researchers found no clear evidence that opinion polarization is increasing on a global scale.

Publication details

A new measure of issue polarization using k-means clustering: US trends 1988– 2024 and predictors of polarization across the world, Royal Society Open Science (2026). DOI: 10.1098/rsos.251428

Citation: Political division in the US surged from 2008 onward, study suggests (2026, February 3) retrieved 3 February 2026 from https://phys.org/news/2026-02-political-division-surged-onward.html

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