 After the outbreak of World War I in 1914, the uncompleted building was confiscated and used as a military hospital and later, until 1923, as barracks by the French occupying forces.Alexander Koenig, who had lost most of his fortune in the aftermath of the war, donated the museum and his private collection to the German government in 1929.The museum finally opened its doors to the public on May 13, 1934.