Complex sentence: From there, he stowed away on an American vessel to Honolulu where, following the American declaration of war, he was exchanged as a diplomat via San Francisco, Halifax and Bergen, finally reaching Berlin on 9 June 1917.
Split into simpler sentences: From there, he stowed away on an American vessel to Honolulu. Travelling via San Francisco, Halifax, and Bergen, he finally reached Berlin on 9 June 1917.