Complex sentence: Germany began by nurturing its prewar links with Indian nationalists, who had for years used Germany, Turkey, Persia, the United States, and other countries as bases for anti-colonial work directed against Britain.
Split into simpler sentences: Germany began by nurturing its prewar links with Indian nationalists. For years, Indian nationalists had used Germany, Turkey, Persia, the United States, and other countries as bases for anti-colonial work directed against Britain.