Is political polarization worse than it's been in the past?

Polarization is debatable — I'll pull the latest data to compare today with past peaks.

It depends on time frame and type of polarization measured - but by most measures of the modern era, yes. By measures of all of American history, no.

1. By measures of the last 50-100 years, polarization is at a modern high

In Congress (elite polarization):

> A Pew Research Center analysis finds that, on average, Democrats and Republicans are farther apart ideologically today than at any time in the past 50 years.

This is measured by DW-NOMINATE scores, which place lawmakers on a liberal-conservative scale based on roll-call voting:

For example, House Democrats moved from about -0.31 to -0.38, while House Republicans moved from 0.25 to nearly 0.51.

Similar academic work using NOMINATE scores finds:

> Following a period of a much more balanced Congress during the middle of the 20th century, ideological distance between the parties began to grow during the 1970s to the extent that Congress is now more polarized than at any time since the late 1870s Reconstruction Era.

One way to see this is the "overlap interval" - how many Republicans are to the left of the most conservative Democrat and vice versa. Today, the overlap interval is zero.

> This was certainly not always true...In the 1960s, for instance, you had intervals where about 50 percent of the legislators in the two parties overlapped.

Since 2002 in the House and 2004 in the Senate there has been no overlap at all between the least liberal Democrats and the least conservative Republicans.

Researchers also note the shift has been asymmetric:

> Polarization among U.S. legislators is asymmetric, as it has primarily been driven by a rightward shift among Republicans

Among the public (mass polarization):

Pew Research Center's long-running surveys find:

> Republicans and Democrats are more divided along ideological lines – and partisan antipathy is deeper and more extensive – than at any point in the last two decades.

Specific trends:

A distinction is often made between:

Studies find:

> In the US, affective polarization has increased more dramatically since the late 1970s than in the eight other countries they examined

And:

> Indeed, by many measures political polarization has been climbing for decades and is at its highest levels in modern history (some analysts say the worst since the Civil War)

2. By measures of the last 200+ years, no - the Civil War era was worse

Many historians and political scientists caution against saying today is the most divided ever:

> Some political scientists have pointed out that — viewed within the context of data from the last two centuries — today's levels of polarization are not such an alarming anomaly compared to those occurring during the time of slavery and similar points along the historical continuum.

> For all the hype about the ruptures and partisan rancor in contemporary American society, the strife pales in comparison with much of the nation's past.

A prominent Civil War historian argues:

> As a historian who has written and taught about the Civil War era for several decades, I know that current divisions pale in comparison to those of the mid-19th century.

Between Lincoln's election in 1860 and Lee's surrender in 1865, the nation literally broke apart, with more than 3 million men taking up arms and at least 620,000 military deaths — the equivalent of approximately 6.5 million dead in 2020. Earlier eras also featured violence inside Congress itself, such as the caning of Senator Charles Sumner in 1856, and secession of seven states after the 1860 election.

Brookings scholars similarly note:

> Today's social conflicts and partisan strife pale in comparison with much of the nation's past. Recall the racial apartheid that scarred America for a century after the end of slavery, and the urban riots and anti-war protests that inflamed the country during the 1960s.

Bottom line

Much of today's increase is driven not just by Americans becoming more ideologically extreme on issues, but by partisan sorting — liberals becoming Democrats and conservatives becoming Republicans — and especially by affective polarization: disliking and distrusting the other side, seeing its policies as a threat to the nation's well-being, even if policy differences have not grown as fast as mutual animosity.