century, resulting in complicated affairs, which were handled by diplomatic means and propaganda as well as by the supreme courts of the Holy Roman Empire.
Cologne lost its status as a free city during the French period. According to the Peace Treaty of Lun�ville (1801) all the territories of the Holy Roman Empire on the left bank of the Rhine were officially incorporated into the French Republic (which already had occupied Cologne in 1798). Thus this region later became part of Napoleon's Empire. Cologne was part of the French D�partement Roer (named after the River Roer, German: Rur) with Aachen (French: Aix-la-Chapelle) as its capital. The French modernized public life, for example by introducing the Napoleonic code and removing the old elites from power. The Napoleonic code remained in use on the left bank of the Rhine until 1900, when a unified civil code (the B�rgerliches Gesetzbuch) was introduced in the German Empire. In 1815, at the Congress of Vienna, Cologne was made part of the Kingdom of Prussia, first in the J�lich-Cleves-Berg province and then the Rhine province.
The permanent tensions between the Roman Catholic Rhineland and the overwhelmingly Protestant Prussian state repeatedly escalated with Cologne being in the focus of the conflict. In 1837 the archbishop of Cologne, Clemens August von Droste-Vischering, was arrested and imprisoned for two years after a dispute over the legal status of marriages between Protestants and Roman Catholics (Mischehenstreit). In 1874 during the Kulturkampf, Archbishop Paul Melchers was imprisoned before taking refuge in the Netherlands. These conflicts alienated the Catholic population from Berlin and contributed to a deeply felt anti-Prussian resentment, which was still significant after World War II, when the former mayor of Cologne, Konrad Adenauer, became the first West German chancellor.
During the 19th and 20th centuries, Cologne absorbed numerous surrounding towns, and by World War I had
