Why did the firebenders only capture the Southern waterbenders?

I-think-the-Firebenders-took-all-of-the-Southern-Waterbenders-because-it-was-closer-to-them-and-because-they-didn't-know-the-location-of-the-Northern-Waterbenders

i think it is because they were so protected like toi side the southern water tribe was easy to get in to and all the men were ether gone ou chould not do eany theing but if the water bendenders chould go over to the southern tribe and they were waterbenders couldn't they have kids ?

Because, they believed that the waterbenders are gona stop them from their plan in conquering the other nations, water beats fire.. and they only captured the southern waterbenders because waterbenders in the northpole is plus stronger because the moon spirit and ocean spirit are with them..

it is because they where not too protected