The dictator's megalomaniacal ambitions made him believe he could conquer the entire world.

megalomaniacal 是由词根 megalo-（表示"巨大的"）和 mania（"狂热、痴迷"）加上形容词后缀 -cal 构成的复合形容词。megalomania 指"夸大妄想症"，megalomaniacal 形容"极度自大狂妄的"，常用来描述独裁者或极端自负者的心理状态。