Since Aang defeated Phoenix King Ozai there has been 2 more Avatars, Korra of the Southern Watertribe, and Terra Katta of the Earth Kingdom Abbey.
Politically speaking much has changed since the last pass of Sozin’s Comet. The world is currently in a state of peace, trading is happening freely across the borders causing the nations to all switch to a single unit of currency, The Credit. Many places still use their older styles of money as well but the credit is accepted almost everywhere world wide.
The Northern Water Tribe is thriving and has split into 3 seperate cities, the original one has doubled in size and the second city is smaller in size and hosts about half its inhabitants. The third city is more of an outpost and less of a “city” hosting a team of about 50 members. The Major city has a great deal of worldly political pull with the other nations, namely the earth kingdom. Life here is easy, many of the people are rich and well to do.
Where as the Southern Water Tribe has grown and become many small tribes scattered across the and. Each one with its own customs and beliefs. Things here are difficult so the people of The Southern Water Tribe pay the rest of the world little mind.
The Air Nomads have begun to repopulate their air temples. They are no longer as segregated as they once were.
Technology has begun to spring up about the most developed parts of the world, such as Bah Sing Se, Central City, and the Fire Nation Capitol. The farther away from these cities you get the less technology you see and even less still is in new or working order. Almost as if to balance the fact that there is more technology in the world many more monasteries have sprung up across the land. These places are free of technology and stick to a more natural approach to the world around them.