Why did they kill all the airbenders?

The アバター Cycle is FIRE-->AIR-->WATER-->EARTH, Souzen killed all the Airbenders because he knew the アバター would be reborn as one, and only he could oppose the 火災, 火 Nation

The 火災, 火 nation was trying to speed up the アバター cycle to get a 火災, 火 nation avatar, the ultimate weapon. They were brainwashing the youth of the 火災, 火 nation to obey the 火災, 火 Lord. Kinda like Hitler. See episode of the Headband. Rules were made for comformity and oaths to the 火災, 火 Lord were sworn. Anyone who didn't obey was sent to the coal mines for the good of the 火災, 火 Nation. Like I 発言しました it was a lot like Hitler.

SO THEY COULD KILL THE アバター BUT IT SUCKS FOR THEM CAUSE HES ALIVE

yes the firelord is just to stupid to think this thru. but mostly i think he tried to wipe them out before aang was born so there were no airbenders for him to reicarnate into. so the cycle was broken.