to increase then decrease in strength, importance, etc. over a period of time （力量、重要性等）兴衰枯荣，盛衰；阴晴圆缺
If something waxes and wanes, it first increases and then decreases over a period of time. [Vs inflect]
Portugal and Spain had possessed vast empires that waxed and waned.
葡萄牙和西班牙都曾是经历了兴衰的大帝国。