some of which were ruled by sovereigns of adjoining regions. Most important of the local rulers were the counts of Nassau-Saarbrücken. Within the Holy Roman Empire these territories gained a wide range of independence, threatened, however, by the French kings, who sought, from the 17th century onwards, to incorporate all the territories on the western side of the river Rhine and repeatedly invaded the area in 1635, in 1676, in 1679, and in 1734, extending their realm to the river Saar and establishing the city and stronghold of Saarlouis in 1680. It was not the king of France but the armies of the French Revolution who terminated the independence of the states in the region of the Saarland. After 1792 they conquered the region and made it part of the French Republic. While a strip in the west belonged to the Moselle department, the centre in 1798 became part of the Sarre department, and the east became part of the Mont-Tonnerre department. After the defeat of Napoleon in 1815, the region was divided again. Most of it became part of the Prussian Rhine Province. Another part in the east, corresponding to the present Saarpfalz district, was allocated to the Kingdom of Bavaria. A small part in the northeast was ruled by the Duke of Oldenburg. On 31 July 1870, the French Emperor Napoleon III ordered an invasion across the River Saar to seize Saarbrücken. The first shots of the Franco-Prussian War of 1870/71 were fired on the heights of Spichern, south of Saarbrücken. The Saar region became part of the German Empire which came into existence on 18 January 1871, during the course of this war. Interwar history In 1920 the Saargebiet was occupied by Britain and France under the provisions of the Treaty of Versailles. The occupied area included portions of the Prussian Rhine Province and the Bavarian Rhenish Palatinate. In practice the region was administered by France. In 1920 this was formalized by a 15-year League of Nations mandate. In 1933, a considerable number of communists and other political opponents of National Socialism fled to the Saar, as it was the only part of Germany that remained outside national administration following the First World War. As a result, anti-Nazi groups agitated for the Saarland to remain under French administration. However, with most of the population being ethnically German, such views were considered suspect or even treasonous, and therefore