Short answers, pulled from the story.
The German colonial empire began in 1884, when Germany claimed its first territories in Africa and the Pacific, and formally ended after World War I through the Treaty of Versailles, which transferred all German colonies to League of Nations mandates in 1919-1920.
Bismarck believed colonial benefits were mostly illusory, that the costs of establishing and maintaining colonies typically exceeded what the homeland gained, and that the German navy was too weak to defend distant territories. He also feared colonies would complicate his European balance-of-power strategy.
The Herero and Nama genocide was carried out in German South West Africa between 1904 and 1908. Lieutenant-General Lothar von Trotha issued the Vernichtungsbefehl (extermination order) after defeating the Herero at the Battle of Waterberg in August 1904. Of an estimated 50,000 Herero, roughly half died; the Nama suffered around 10,000 deaths, also close to half their population. It is recognized as the first genocide of the 20th century.
Within a single year after 1884, Germany assembled the third-largest colonial empire in the world, surpassed only by Britain and France. Its territories stretched across parts of Africa and Oceania.
Bernhard Dernburg, who became head of the Colonial Department in September 1906, abolished corporal punishment, established public schools and hospitals in every colony, extended rail lines into the African interior, and secured capital investment with public funds. Between 1906 and 1914, total trade between Germany and its colonies rose from 72 million marks to 264 million marks, and colonial tax income increased sixfold.
Under the Treaty of Versailles, German colonies were transformed into League of Nations mandates divided among Belgium, Britain and its Dominions, France, and Japan. Of the roughly 12.5 million people in the colonies in 1914-42 percent passed to British and Dominion mandates, 33 percent to France, and 25 percent to Belgium. Germany was stripped of all colonial possessions permanently.