This phrase went out at Versailles during the period of Louis XIV. With Bourbons reigning in Versailles and Madrid, even if the two nations never unified, French influence would run within -almost- the whole European Continent. Therefore, Louis XIV used this word to mean that the natural border, the Pyrenees mountains, is no longer a meaningful border between Spain and France.

I guess these words prove that the French empire was the leading power in Europe at that time.

These words prove that at that time France was the leading power in Europe.

Louis the XIV said this in the aftermath of the War of the Spanish Succession. It is right that it proves how powerful they were, however, you should notice that England was the most beneficial country from the war. They became a great power in the aftermath of the war.