Germany 1919-1990
1921
In 1918 Germany and its Central allies lost World War I. A revolution ended the monarchy in the Realm and all of its constituent states. A Republic was declared that was still called the German Realm. Its National Assemblee at Weimar adopted a democratic constitution, hence the term "Weimar Republic". The Republic had a Social Democratic governement for the first years, led by President Friedrich Ebert.
The Versailles treaty of 1919 that ended World War I left Germany decimated and humiliated. If you compare this map to the map of 1871, you will see that large parts of the German Realm were ceded to neighbouring countries like revived Poland, (West Prussia and Upper Silesia and Posen) Denmark, (North Schleswig) Belgium (Eupen and Malmedy) and France (Alsace-Loraine). East Prussia was now seperated by a corridor that gave Poland access to the Baltic sea. Two of Germany's Baltic ports were given to the Leage of Nations. Danzig, where Poland had a say in the Governement of the City, and Memel that was annexed by Lithuania in 1923. Some of these transfers were the subject of a plesbiscite. Germany retained a part of Upper Silesia, The Masuren region of East Prussia and a part of North-Schleswig through these plesbiscites.
Furthermore Germany was blaimed for the War and forced to pay huge reparations to the allies. Its airforce was desolved and it was only allowed to have a nominal army and navy.
The Saar Basin (indicated by the red dots) was made a protectorate of France, although formally remaining a part of the Realm. France was given the exploitation of its coal and iron ore mines.After fifteen year their should be a plesbiscite. The lands West of the Rhine, and some bridgeheads East of the Rhine were occupied by the allies for periods varying from five to fifteen years (indicated by the light-blue line). Germany was not allowed to have any military activity in a zone 50 km. east of that line. After the occupation would be over, the Rhineland should remain demilitarized.
These humiliating circumstances, that had to be accepted by the new Republic, made the new regime very unpopular among nationalistic and conservative Germans. Revanchism and the notion that the Republican Revolution of 1918 was the real cause of the lost war, the German Army being unbeaten in the field up until then (a fallacy known as the "Legend of the Dagger blow") made many Germans deeply resentfull of the new governement. Communists and right-wing nationalists would from time to time attack the new democracy.
Economic crisis and the huge reparations that had to be payed, ruined Germany quickly. When reparations could be payed no longer this caused France to occupy the industrial Ruhr area (indicated by the light-red line). The governement declared a general strike in the newly occupied areas and started to print money, causing the inflation to take ridiculous proportions (a stamp was now wort a few billion Reichsmarks). France had to give up the Ruhr occupation. After that the German economy was allowed to stabilise. The harshest measures were given up by the allies.
Notably the new democracy and former enimy was not allowed to become a part of the system that the allies had envisaged. Unlike France after the Napoleonic wars it was not allowed to take its place in the new post-war system. This would have desastrous consequenses.