What are the Night King's motives?
Seriously, I don't get this guy. What does he want? Why is he massing armies and marching on unconquered lands?
The Kings and Queens either want to improve the lives of their people and the people they'd conquer/liberate (good guys) or to enrich their own lives (bad guys). Neither of those motivations seem to apply to the Night King. His armies don't celebrate victories with weeks of feasting and frolicking. He himself doesn't seem given to feasting and frolicking. He doesn't need to feed his starving subjects. Their leisure activities seem to run the gamut from staring woodenly ahead to trudging woodenly ahead.
Is "I'm tired of staring at snow / trudging through snow" really a good reason to start a war?