The colony of German East Africa was established in 1885, and in time included what is now Rwanda, Burundi, and Tanzania.
German East African stamps were originally regular German issues with overprints; eventually Germany began printing stamps especially for the colony, including the famous ‘yacht’ stamps. The colony lasted until World War I.
Note: The German name for the colony is Deutsch-Ostafrika; sales listings on this site may use that name instead of the English.