Historically, every time inequality reached this level it led to civil war and revolution.

This is a universal historical claim: every past episode of inequality at roughly today's level led to civil war and revolution. True: historical and economic-history research (for example long-run inequality datasets, or studies such as Scheidel's or Turchin's) shows that essentially every documented episode of comparably high inequality was followed by civil war and/or revolution, with no clear counterexamples. Mostly true: the pattern holds in nearly all cases, with only one or two marginal exceptions. Mixed: comparable inequality was followed by civil war or revolution in roughly half of the documented cases. Mostly false: some real association exists between extreme inequality and later violent upheaval (for example, inequality fell after wars, revolutions or state collapse), but there are many documented episodes of comparable inequality, such as the US Gilded Age or 1920s, that did not lead to civil war or revolution. In that case the claim overstates a correlation as a rule, or reverses which came first. False: the research shows no meaningful link between high inequality and later civil war or revolution.

Set before the research began.

1. E1 Why class inequality breeds coups but not civil wars Journal of Peace Research (Oxford Academic); author Christian Houle, Michigan State University · 27 July 2016

   “Using data on 128 developing countries between 1960 and 2008, I find that while class inequality fosters coups, it has no discernible effect on civil wars.”

2. E2 Why class inequality breeds coups but not civil wars Journal of Peace Research (Oxford Academic); author Christian Houle, Michigan State University · 27 July 2016

   “Class inequality, however, breeds other forms of political violence. In particular, it increases the likelihood of military coups.”

3. E3 Inequality and Conflict: A Review of an Age-Old Concern UNRISD (United Nations Research Institute for Social Development), Identities, Conflict and Cohesion Programme Paper No. 11, by Christopher Cramer (SOAS) · October 2005

   “The upshot is that there are no grounds for accepting any “event regularity” holding across countries when it comes to inequality and its consequences for violent conflict.”

The evidence finds no discernible effect of class inequality on civil wars in developing countries from 1960 to 2008, with a link to coups [E1, E2], and no cross-country regularity between inequality and violent conflict [E3]. It does not look at past episodes of inequality comparable to today's, or at revolution, which the criteria require to settle the claim.