When under the influence of certain (or some) reasons (or causes) (alcohol, war, etc - added Spir here) the low instincts are unbridled (or unrestrained), the brute appears (or come forward, "apparait", Fr. ) and rule over (or dominate), stifling every ("toute", Fr. ) noble, generous impulse; it is then the ruin (or downfall or decline) of any humanity in man.
You either choose to view America as the shining city on the hill that inspires the best in all mankind, or you don't.