same = savagery as mention in the 前一句.
may be said = said = equal to
laying waste = wasting,plundering,robbing by force
held by = controlled
The whole sentence = The action of intentional robbing,killing civilians and destroying a country by force because it could not be controlled by the occupying forces was a savage act done by savages and it should not have happened in a war of a civilized world.(This seems to described the Japs in China)