Twenty years.
For twenty years, there was peace. For twenty years, tranquility had roamed through the four nations at the sight of the returned Avatar. Fire Lord Zuko, Katara, Toph, Sokka, Suki, and Aang had parted their separate ways; only meeting up with each other for a reunion once every few years. Sokka had become the chief of the Southern Water Tribe after his father, but had to give the title to Katara when he left for the Earth Kingdom with Suki, his newly betrothed wife. Katara, too, had gotten married, but to a strong Waterbender, Blane. He was of the Northern Water Tribe. Zuko had gotten married to Mai sometime after he was crowned Fire Lord, giving birth to their first-born son. Toph, despite being the youngest, was the only one in the group the gave birth to multiples. She had twins, the father being a warrior for the Earth Kingdom. Toph does not like to talk about him, as he died for unknown reasons sometime after the twins were born. Aang was the only one whom remained unmarried. Katara had waited for him to settle down, but when he hadn't, he had lost his only love. Aang had been busy working with Zuko to get the Fire Nation back in order. The Fire Nation was on the right track for the first time in a long time, when it happened.
Fire Lord Zuko had captured Aang. Twenty years later. The Avatar didn't need to be placed in complete lock down, because he was compliant. He saw Sokka and Suki, both of them captured during a raid in the Earth Kingdom. Kyoshi was burned down again, and the whole town was taken hostage. Aang knew that if he fought, they would surely die. And if Sokka died, he knew that Katara would be following soon after. The Avatar was remorseful for letting the world down, because it then led to a war. From the prison guards talking, Aang heard of the Dai Li wanting to share the Fire Nation's glory. After all, they were fighting alongside them for twenty years now. The Fire Lord refused to share domination with them, ergo a war broke out. The Dai Li took back Ba Sing Se, Kyoshi, and Gaoling. With having a few major cities already, it sparked encouragement for the agents. Soon, the Fire Navy was fighting to take back their previously conquered country. Aang was enraged with what Zuko had done, but he was in no position to take charge of anything.
When Katara heard the news, she head to the Earth Kingdom in search of old friends and family. Blane was left to watch the tribe while she was gone. Toph was not surprised of their ex-ally, as she said she 'expected as much from a Firebending loser-boy'. The Earthbender told Katara that her brother and sister-in-law were taking captive by the Fire Nation. Katara didn't want to believe it at first, but it was true. As soon as peace was restored to the world, the Fire Nation, of course, had to act up. Again.
Toph had created an underground shelter, where she let neighbors, friends, and anyone else who she trusted thrive. But as the months passed, the crowd diminished to five people. A small family of only two people, father and daughter, were the only survivors other then Toph's family. The father's name was Hiro and the daughter's name was Ayame. But now, with Katara, the survivors added up to six.
Exiled Fire Lord Ozai was never released from prison. He did, however, begin to think differently of Zuko. Azula was still classified as mental, but she had calmed down over the years. She wasn't as on edge, but she was still controlling. Doctors said that it indicated that she was still having trouble letting go of the past, so Princess Azula stayed in the therapeutic home for crazies. But she had been given some extra freedom for her hard work; she was allowed to go out to town with a guard. She could have daily spars, too. But there was a small slip during those twenty years; they realized that Azula had been gone for a good time. The patient that they had been treating was none other then a trusted Dai Li agent. When caught, the agent was sent to prison for life, under maximum security. The Azula incident was kept under wraps, especially because they didn't want the Fire Lord knowing that they mistaken a friend as the princess. At least she wasn't doing anything insane that would have her arise to the public. What Fire Lord Zuko didn't know was that his sister hadn't been on an insanity watch for fifteen years.