Since 1945 big, rich, developed countries have not waged war on each other.

Judge as of 2012-11-01. TRUE: between 1945 and 2012 there was no interstate war (by standard definitions, e.g. Correlates of War: 1,000+ battle deaths) in which large, wealthy, developed countries (e.g. great powers, the US, Western Europe, Japan, the USSR/Russia as a great power) fought each other directly. MOSTLY TRUE: no such full war occurred, with only marginal edge cases, e.g. brief clashes below the war threshold, or conflicts where whether a party counts as 'rich, developed' is debatable (such as the 1974 Cyprus conflict or the 2008 Russia–Georgia war). MIXED: one or more clear wars between such states occurred, but they were few and limited. MOSTLY FALSE: several clear wars between big, rich, developed countries occurred in the period. FALSE: such countries fought each other frequently, at rates similar to before 1945.

Set before the research began.

1. E1 Nothing unusual about 'the long peace' since WWII University of Colorado Boulder BioFrontiers Institute · 26 February 2018

   “In contrast, during the long peace of the 1940–2003 post-war period, there were only 5 large wars — about one every 12.8 years.”

2. E2 Statistical sightings of better angels: Analysing the distribution of battle-deaths in interstate conflict over time Journal of Peace Research (Oxford Academic), by Håvard Mokleiv Nygård, PRIO · 1 March 2020

   “While the empirical pattern constituting the long peace is not in itself disputed, some recent investigations have questioned whether the pattern can be said to constitute a statistically established trend”

3. E3 The West, Russia and European security: Still the long peace? - Andrew Cottey, 2022 SAGE Publications (The British Journal of Politics and International Relations) · May 2022

   “In all these crises, both the major Western powers and Russia have behaved with restraint and to varying degrees taken concrete steps to avoid escalation to direct conflict with one another.”

4. E4 Statistical sightings of better angels: Analysing the distribution of battle-deaths in interstate conflict over time Journal of Peace Research (Oxford Academic), by Håvard Mokleiv Nygård, PRIO · 1 March 2020

   “The Falklands war, for instance, is included in the CoW interstate wars dataset with 1,001 battle-deaths, even though the actual number is most likely closer to 900”

A peer-reviewed article states that the post-WWII 'long peace' pattern is not in itself disputed, though some recent investigations question whether it is a statistically established trend (E2). A university report counts only 5 large wars in 1940–2003 (E1), and an academic article says that in the crises it discusses, the major Western powers and Russia behaved with restraint and took steps to avoid escalation to direct conflict with one another (E3). The one cited war involving a developed country, the Falklands war (UK vs Argentina), only just meets the Correlates of War threshold, and its actual battle deaths were likely below it (E4). It is an edge case because Argentina's standing as a big, rich, developed country is debatable. The evidence does not name each of the 5 large wars or confirm the claim directly for the whole Cold War, so the support is fairly indirect.