Answer: D
Explanation
‘While’ here indicates that something opposite follows. So, while war has never been entirely absent, there have been some periods that appear remarkably peaceful. Hence, ‘serene’ or ‘pacific’ might suit the second blank. But serene is coupled with ‘posterity’, which means ‘future generations’ and so does not fit.
(archives = documents or stored records; ambivalent = vague; serene = peaceful; desultory = intermittent; annals =
records or chronicles; pacific = peaceful; belligerent = aggressive)