Very interesting! That would create quite a dataset… all the places people have ever bombed. Were you thinking of just war-related bombing in modern ages, or including historical sieges of cities (i.e., the Mongols, etc.), or terrorist attacks, etc.?
Also… could we accomplish this without a separate layer, using tags and queries? This question is relevant to quite a few datasets, where thematic information should be grouped and categorized, but that doesn’t belong in a relation.