Over the course of six seasons of Game of Thrones, we have learned about White Walkers in dribs and drabs. The first two seasons confirmed their existence & threat and then season 3 showed us that they can be killed by dragonglass. In season 4, we saw that the Night King can turn a human baby into a white walker. Next season showed us that they can be killed by Valyrian steel & how they raise the dead and in season 6, we learned about their origin. And now in episode 6 (Beyond the Wall) of season 7, we got some vital information on how they can be defeated.
The moment arrived when Jon Snow & his team ambushed a group of White Walker & wights and when Jon killed the White Walker, most of the wights also perished. This means that if you kill a White Walker, the dead that he raised also die. And who has raised the most number of wights? The Night King himself. This makes it a pretty simple equation for Jon- Kill the Night King and The Great War will be over. Although that’s easier said than done.
How will Jon Snow & his A-team use this information to their advantage? We will probably have to wait until the final season to find out.