Why balanced war histories take longer than twenty years

How long after a major war does it take for relatively unbiased histories to appear?

Serious attempts may begin after about twenty years, but even-handed criticism often takes much longer because personal and national loyalties persist.

The first generation after a war can recognise mistakes, but it rarely applies scrutiny evenly. Scholars are more comfortable assigning blame to people outside their own intellectual or national loyalties. Attempts at balance may emerge after roughly twenty years, while genuinely dispassionate work can take much longer, often until the participants and their immediate defenders are gone. Propaganda aimed at domestic and foreign audiences further complicates the surviving record.