Not quite true - particularly of WW2 where is was big and long. Dresden, Hiroshima, Russian treatment of German prisoners etc. The list is very long. And where do you draw the line between aggressor and defender? Were Germany and Japan the aggressors in 1945? New Zealand helped defend the UK, as did many dominion nations. However while the threat to New Zealand was felt (from Japan), it was hardly playing the role of a defender (and declared war on Germany before the UK did). This position is common in many conflicts.