From Dark Horse:
When Aang leaves to aid Fire Lord Zuko with spiritual affairs in the Fire Nation, Katara and Sokka return to the Southern Water Tribe by themselves, where they are shocked to discover that their village has become a bustling city, with Hakoda in charge. The changes seem to have largely been due to the efforts of Malina, a member of the Northern Water Tribe who is seemingly striving for greater unification of the Water Tribes, but has unknown intentions.