|Oodalak gets Korra to open the portal at the south pole which allows the spirits of the south to once again dance in the sky, creating the "Southern Lights", just like how the north has the "Northern Lights".. but that's only the first step. This portal will allow free travel between the north and south, and unify them back into one tribe... He starts getting his troops to invade the south tribe in order to stop them from interfering with the spirits.. it almost seems like he's a bad guy now, but I'm not entirely sure..|
.. Yep, I was right. Korra found out that Oodalak framed her dad so he could become chief of the northern water tribe. Now he's trying to take over the south. Korra was trying to avoid a war up until now, but now it looks like there's no other choice.
Korra fails at getting Republic City to send troops to help the south, and breaks up with Macco because he ratted out her plan to get the troops there unofficially.. So she goes off to the fire nation to ask their help instead.. but she gets ambushed by a giant spirit, gets knocked out, and then ends up on a fire nation island with amnesia.
Meanwhile, Macco is investigating the attacks at Republic City that have been linked to the north water tribe. He thinks there's more to it than that, because of clues that some fire bending technology was involved.. but the rest of the police force won't listen to him... Eventually he finds out that Berrik, the guy who's been helping Asami/Future Industries and started shooting a movie to help promote supporting the south... he's the one behind the recent attacks.
This plot is getting really complicated and hard to sum up... it's even simultaneously showing other unrelated plot threads, like Tenzin's family issues and stuff.