Question: In which country did Anton Ludwig August von Mackensen lead an Army Group from 1916-1918?
Sentence (from "Army Group Mackensen (Romania)"): The Army Group Mackensen (German: "Heeresgruppe Mackensen") which operated against Romania between 28 August 1916 and 7 May 1918 during World War I under the command of Field Marshal Mackensen, was an Army Group of the German Army.
Relevant evidence: Yes