1. The licentious monarch helped bring about his country´s downfall.
    这昏君荒淫无道, 加速了这个国家的灭亡。

2. His downfall was caused by gambling and drink.
    他的垮台是由赌博和酗酒造成的。

3. A long-lost brother, who was presumed dead, was really alive all the time and wickedly plotting to bring about the hero´s downfall. And so on.
    主人公一位长期失散的兄弟，大家都以为死了，实际上一直活着，并且正在策划暗算主人公；如此等等，

4. Gambling was his downfall.
    赌博是他堕落的缘由。