Final answer:
The Seven Years' War was the conflict in which King Louis invested, leading to the collapse of the French Empire and a rearranged balance of power in Europe.
Step-by-step explanation:
King Louis invested in the Seven Years' War (1754-1763), which marked the collapse of France's empire.
The Seven Years' War established a new balance of power in Europe where Britain emerged as the dominant power, leading to France losing its imperial possessions.
The Peace of Hubertusburg led to Britain gaining territories in North America and India from France, while Spain surrendered Florida and France gave control of the Louisiana Territory to Spain, leading to a weakened French Empire and strained resources.