Why did France not want the unification of Germany?

As in early times, European states were in conflict with each other. There has always been a rivalry between them regarding trade and other activities. France did not want the unification of Germany, because after that the state could become stronger and oust French products from the markets. This rivalry was justified because in those days the trade monopoly mattered so much. The unification of Germany became an inevitable process. After that, the centralized state improved the economy and surpassed many countries.