Ultima III: Exodus/Second Quest

Between Ultima 3 and Ultima 4
After the defeat of Exodus many cataclysms changed the shape of Sosaria. After these dramatic events, Lord British established a system of Principles and Virtues and re-founded Sosaria with the name of Britannia.

Characters:
 * Iolo, Dupre and Shamino became embodiements of three of the eight Virtues: Compassion, Honor and Spirituality, respectively; in Ultima 4 they will join the Stranger as his Companions on the Quest of the Avatar.
 * Sentri became Lord of Serpent's Hold, the castle that protects the principle of Courage.
 * Gwino/Gwenno moved from the Castle to the nearby city of Britan, where she kept being a bard. She will become a playable character starting from Ultima 5.

Locations:
 * Lord British Castle and the Royal City Britain kept being the center of the Britannia, the new name of Sosaria.
 * Yew kept its name and its location in the deep forest.
 * Moon became Moonglow and it kept being close to the Moon Gate of the new moon.
 * The inhabitants of Montor East, Montor West and Fawn didn't accept the system of Principles and Virtues established by Lord British. They left Sosaria and founded new cities on Serpent Isle (Ultima VII part 2: Serpent Isle).
 * Grey, Devil Guard and Death Gulch were destroyed in the cataclysms that followed the defeat of Exodus.
 * The magic town of Dawn ceased its appearances for a long time. In Ultima 9 the ruins of a village named Dawn can be found: it was destroyed by a red dragon.
 * The Isle of Fire, location of Exodus Castle, became a barren islet (Ultima IV: Quest of the Avatar) and ultimately sank into the sea (before Ultima V: Warriors of Destiny). It will reappear long later, as the location of the Forge of Virtue.

Races:
 * Bobbits and Elves disappeared forever from Sosaria.
 * Fuzzies disappeared too, although it is speculated that the Emps featured in Ultima VII: The Black Gate may be connected to them.
 * Dwarves became so rare they were thought to be extinct as well, until Ultima Underworld: The Stygian Abyss (between Ultima 6 and Ultima 7).

Sven Carlsberg's Second Quest
The game version by Sven Carlsberg features a second quest that starts after the normal game is completed. The story tells some of the events that happened between Ultima 3 and Ultima 4.