Short answer: In the United States, polarization today is higher than in the late 20th century and near modern-era highs by several key measures, but it is not unprecedented in all of U.S. history (the Civil War/Reconstruction era was worse in terms of open conflict). Globally, trends vary: some democracies show rising polarization, others do not.
What the evidence shows (mainly U.S.):
•Elite (Congress) polarization: Roll-call data (e.g., DW-NOMINATE) show the parties have moved far apart since the 1970s, with almost no ideological overlap between Democrats and Republicans today—levels comparable to or exceeding those seen since the late 19th century.
•Affective polarization (how much partisans dislike the other side): Survey measures have climbed sharply since the 1980s. People rate the other party more negatively, are less willing to socialize or marry across party lines, and perceive greater moral distance.
•Mass issue positions: The public has not uniformly become more extreme. On many issues the distribution remains moderate, but party “sorting” has increased—partisans line up more consistently across issues, identities, and geography, leaving fewer cross-pressured voters.
•Electoral behavior: Split-ticket voting and cross-party incumbency advantages have fallen; straight-ticket voting and safe districts/counties have risen, reinforcing partisan separation.
Historical perspective:
•Worse than mid-20th century: The 1930s–1970s had low measured congressional polarization due to cross-cutting coalitions (e.g., conservative Southern Democrats, liberal Northeastern Republicans).
•Not uniquely worst ever: The 1850s–1870s featured extreme sectional polarization and violence. Today’s polarization is severe in legislative behavior and social animosity but not at Civil War levels of conflict.
•Conflict vs. cooperation cycles have recurred; the mid-20th century was an unusually depolarized period.
Outside the U.S.:
•Affective polarization has risen more in the U.S. than in many peer democracies. Some countries show increases (e.g., UK post‑Brexit, parts of Eastern Europe), while others have been stable or even less polarized depending on the metric and time frame.
Bottom line: Compared with the late 20th century, U.S. polarization—especially among elites and in partisan animosity—is markedly worse. In the very long view, it’s not unprecedented, but it is high enough to affect governance, media consumption, and everyday social relationships.
If you had a specific country or type of polarization in mind (elite, public opinion, or social/affective), I can tailor the answer and share representative charts.