Great powers and developed countries have stopped going to war, and worldwide deaths in warfare may be at an all-time low.

Judged as of 2011-11-10. Two parts: (a) great powers and developed countries have stopped fighting wars, read as wars between one another, given the claim's context of the 'Long Peace' since 1945; (b) worldwide battle deaths (hedged 'may be'), in absolute or per-capita terms, are at or near their lowest level on record. True: datasets such as UCDP/PRIO or the Correlates of War show no war directly between great powers or developed states for decades up to 2011, and global battle-death rates near the 2000s low. Mostly true: both hold broadly, with minor exceptions (for example brief or limited clashes, or developed countries fighting wars against non-developed states). Mixed: one part is supported and the other is not. Mostly false: both rest on a real trend but are substantially overstated, for example by ignoring major wars fought by developed countries. False: the data show recent wars between great powers or developed states, and battle deaths well above historical lows.

Set before the research began.

1. E1 War Has Almost Ceased to Exist: An Assessment Political Science Quarterly (article by John Mueller, Ohio State University faculty page)

   “However, the data so arrayed actually mask what is likely to constitute the most significant number in the history of warfare: zero (or near-zero). This is the number of wars that have taken place since 1945 between developed states”

2. E2 War Has Almost Ceased to Exist: An Assessment Political Science Quarterly (article by John Mueller, Ohio State University faculty page)

   “The Cold War of 1945–1989 generated several international wars waged between developed states and states or entities in the developing world.”

3. E3 Long Peace - Wikipedia Wikipedia

   “there has been a continued absence of direct conflict between any of the largest economies by gross domestic product; instead, wealthier countries have fought limited small-scale regional conflicts with poorer countries.”

4. E4 Long Peace - Wikipedia Wikipedia

   “the number of international wars decreased from a rate of six per year in the 1950s to one per year in the 2000s, and the number of fatalities decreased from 240 reported deaths per million to less than 10 reported deaths per million.”

Mueller's assessment (E1) puts the number of wars between developed states since 1945 at zero or near zero, and the Long Peace entry (E3) describes no direct conflict between the largest economies. Both sources also say developed or wealthier countries kept fighting wars and smaller conflicts against developing states (E2, E3), which the criteria treat as a minor exception. On battle deaths, E4 reports that international war fatalities fell from 240 per million in the 1950s to under 10 per million in the 2000s. That supports the hedged 'may be at an all-time low' in per-capita terms, but it comes from a secondary summary rather than a dataset that shows a record low. Both parts broadly hold, with the exceptions the criteria allow for.