<p>Cant be certain but... </p><p>The war wasnt so "hardcore" or "brutal" as it just started during Hamas time. They didnt kill Hama and the prisioners, but with the waterbenders in captivity they had no way of stopping the war later on. This also stops them from reproducting more water benders, although the ability found its way to Katara. </p><p>During Kyas time, the war has gotton alot worse. When Katara was announced an waterbender and Yon Rha was sent to capture her, Yon took the simple easy way and killed her on the spot, rather than imprisioning her. As Katara says during her revenge, she would have went easier on him if he imprisioned her rather than murder. </p>

<p>If I had to guess, it could be that the Fire Nation wasn't sure if Aang had reincarnated yet, and was playing it safe by keeping a close eye on the Water Tribes in case a succeeding Avatar revealed his/herself as one of the waterbenders. As they couldn't mount an assault for years in the North due to its defenses, they focused on the South, and kept the waterbenders alive in case one of them showed signs of being the Avatar (and could be in turn kept alive to stop him/her from reincarnating). </p><p>As for why Yon Rha killed Kya, I would bet on the reason being he was a cold, cruel sadist who had no interest in capturing prisoners. He probably wasn't aware of any grand plan other than his orders to keep an eye on what remained of the Southern Water Tribe. </p>

<p>Im surprised Sozin tried to hunt the Avatar for such a long time after the Air Nomad Genocide </p><p>Remember: Avatars arent usually told they are the Avatar until they are like 16, and Aang was told this when he was like 12. Why didnt the Fire nation think they actually killed the Avatar in the Air Nomad genocide, the Avatar is no different from the others until they are taught to bend other elements. Similar to how Roku was just an fire nation noble, he wasnt seen as anything special until he turned 16 and was told he was the Avatar </p>

<p>My guess is he was counting on the Avatar State to trigger during the genocide to identify the Avatar. Even if the Avatar hadn't been told of his destiny, the defense mechanism would have probably still triggered with the Avatar and his loved one's lives in danger. </p><p>Since he heard no reports of glowing tattoos, Sozin probably figured the Avatar had somehow escaped, thus his frantic searching. </p>

<p>Generally, when a nation is attempting to subdue a hostile population they do two things. First, they disarm them. Benders are essentially human weapons from a military perspective, so they have to be removed from the field. Second, you take hostages to ensure cooperation. That is likely why they captured waterbenders rather than killing them in the past. Given their importance in Water Tribe culture, the SWT likely wouldn't risk large-scale action against the Fire Nation if the lives of their benders were on the line. Of course, by the time Kya was killed, the SWT were no longer a real threat to the Fire Nation. They didn't need them to 'stay down'. So killing the last waterbender was simpler than capturing her. </p>

<p>All brilliant ideas! Thanks, guys for the help. Truly this fanbase is better than most. :) </p>

<div class="quote"><i>AvatarMako wrote:
All brilliant ideas! Thanks, guys for the help. Truly this fanbase is better than most. :)</i></div>
<p>Dont worry, I was flamed in a PvZ wiki forum because I didnt believe turnips were bronies </p> As much as the Avatar state being an emergency state, the fire nation would probably still not rely on seeing the Avatar in such state. Why? Remember how Roku couldnt enter the Avatar state for such a long time? Much after he was even announced the Avatar? Many Avatars couldnt enter the Avatar state even during emergencies, such as the time Korra was blood bent then stripped of bending abilities<figure class="article-thumb tright show-info-icon" style="width: 180px"> <figcaption> <p class="caption">The neutralization process</p> </figcaption></figure>

<div class="quote"><i>Thinklogic wrote:
<div class="quote">AvatarMako wrote:
All brilliant ideas! Thanks, guys for the help. Truly this fanbase is better than most. :)</i></div>
Dont worry, I was flamed in a PvZ wiki forum because I didnt believe turnips were bronies As much as the Avatar state being an emergency state, the fire nation would probably still not rely on seeing the Avatar in such state. Why? Remember how Roku couldnt enter the Avatar state for such a long time? Much after he was even announced the Avatar? Many Avatars couldnt enter the Avatar state even during emergencies, such as the time Korra was blood bent then stripped of bending abilities<figure class="article-thumb tright show-info-icon" style="width: 180px"> <figcaption> <p class="caption">The neutralization process</p> </figcaption></figure></div> <p>Good point. So in that case, why do you think the waterbenders were kept alive? Is it possible that some of them served a purpose,  forced to use their powers to help the FN in some ways? </p>

I was thinking either a rouge water bender army. Or having prisoners as black mail. They would threaten to kill prisoners if the water tribe didn't give up land or something.