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

Is polarization worse today? I'll pull the latest research to put current levels in historical context.

Political polarization is worse than it has been in the recent past - in modern and post-World War II history - but not necessarily worse than at all points in American history.

1. At record highs for the modern era

Among both elected officials and the public, multiple measures show polarization at modern highs:

> Political elites of the United States are deeply polarized. Polarization of the Democratic and Republican Parties is higher than at any time since the end of the Civil War

> The results from DW-NOMINATE indicate that the level of polarization in Congress is now the highest since the end of the Civil War and shows no sign that it will abate

Other analysis phrased it as Congress "now more polarized than at any time since the late 1870s Reconstruction Era", following a period of a much more balanced Congress during the middle of the 20th century. This reflects the disappearance of overlap: "Today, the overlap interval is zero" while "In the 1960s, for instance... about 50 percent of the legislators in the two parties overlapped"

2. Affective polarization has surged

Affective polarization — the gap between positive feelings toward one's own party and negative feelings toward the opposing party —

> has increased markedly in the past two decades

In a multi-nation comparison:

> They found that in the US, affective polarization has increased more dramatically since the late 1970s than in the eight other countries they examined—the UK, Canada, Australia, New Zealand, Germany, Switzerland, Norway, and Sweden

Using feeling thermometers 0-100: "In 1978, the average American rated the members of their own political party 27 points higher than members of the other major party. By 2016, Americans were rating their own party 45.9 points higher than the other party, on average"

A Stanford-linked study also found: "Over the past four decades, the chilly chasm of negative sentiment between Democrats and Republicans in the U.S. has nearly doubled, and it has grown faster and larger compared to the partisan climates of eight other" democracies

3. Historical context: Not unprecedented

While current polarization is exceptional in recent decades and compared to other democracies, historians and political scientists note it is not unprecedented when looking at 200 years of history:

> 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

Longer historical view suggests:

> 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... There have been long stretches of American history in which conflicts were far worse

The 1850s slavery era, the Civil War, and the late 19th century (1870-1900) are often cited as equally or more polarized periods. The current period is distinctive because conflict has become largely one-dimensional along the liberal-conservative / partisan line, with regional cross-cutting divisions that once dampened conflict having largely disappeared, and because both ideological divergence and affective dislike now align closely with party identity.