Complex sentence: At the Versailles Conference, Portugal regained control of all its lost territory, but did not retain possession (by the principle of uti possidetis) of territories gained during the war, except for Kionga, a port city in modern-day Tanzania.
Split into simpler sentences: At the Versailles Conference, Portugal regained control of all its lost territory, however it did not leave uti possidetis. Portuguese gains included Kionga, a port city in modern-day Tanzania.