In Westeros. the Seven Kingdoms is ruled by the one who walks the steps & sits the Iron Throne. The Iron Throne is helm of the world since Aegon the Conqueror first forged the Iron Throne with a thousand swords of his enemies in the breath of fire by his dragon, Balerion the Black Dread. 
Now nearly three hundred years after the death of Aegon the Conqueror, Houses of Westeros fight endlessly for or against the Iron Throne; House Targaryen, Stark, Lannister, Baratheon, Tyrell, Mormont, and many others. 
However the world of Westeros does not know there is a greater threat than who sits the Iron Throne. 
A true enemy to the world of the Living lies beyond the North of the Wall guarded by the Night's Watch & the Wildlings living in the wild lands beyond the Wall. 
In the deep North, there is a land of always winter with an untold power by the ruler of the Dead of White Walkers & Wights, the Night King. The Night King has been waiting silently for thousands of years to destroy the world of the Living.
The Wall has been broken through with hundreds of thousands of Dead marching past, destroying everything & everyone in their path; death. The Night King will cover the world in cold darkness and a night that never ends; the Long Night. 
Jon Snow, bastard of House Stark & King of the North and Queen Daenerys Targaryen, Mother of Dragons sail for Winterfell for the battle of the Long Night against the Night King. They know the Great War is the only war that matters and it is here. They're aware of the challenges ahead and what it could cost the Living. 
Many question how the Long Night began & how it will end. Until the Night King is destroyed, the Iron Throne matters not. But others do not focus on the army of the Dead. Rather they focus on what the Mother of Dragons, Queen Daenerys Targaryen will do if she claims her ancestry seat, the Iron Throne. It'll cause the ruin & death of the people of the world if they do not unite as one against the Dead.
Who will prevail?