Alsace-Lorraine as a single political division was a creation of the German government in 1871; the two districts have different origins and a different history, indeed each of them is made up of parts with histories still further separate and distinct. All have in common the fact that they form part of a region which since the ninth century has been debated ground between Germany and France. In the sixteenth, seventeenth, and eighteenth centuries the territory which now forms Alsace and Lorraine was acquired bit by bit by France; in 1871 it was transferred in one lump to the new German empire. In the later Middle Ages Lorraine formed a duchy, within which lay a number of small and in some cases independent feudal states and the city of Metz, a free city of the Holy Roman Empire whose people spoke French. In 1552, on the petition of certain German Protestant princes, Metz was placed under the protection of the king of France, who took possession of the city and the surrounding territory subject to it. In 1613 the bishopric of Metz and its lands were taken over by the French king, the whole being combined with Toul and Verdun into the province of the Three Bishoprics (Trois Evêchés), and the cession was confirmed by the Emperor in the treaty of Westphalia of 1648. Further acquisitions made in the seventeenth century, notably Sierck and Saarlouis, gave France a strategic line of communication through Lorraine to Alsace. The duchy of Lorraine, which had likewise been dependent on the Holy Roman Empire, was declared free by Emperor Charles V and was gradually drawn into the French sphere of influence. Relinquished by its Hapsburg duke in 1736, in 1738 by the treaty of Vienna it was handed over to a Polish duke, Stanislas Leszcynski, on condition that at his death it should pass to his son-in-law, Louis XV of France, by whom it was accordingly acquired in 1766. Certain small enclaves within Lorraine did not pass to France until the Revolution.