Complex sentence: At the Wall, Melisandre resurrects Jon Snow who is reunited with Sansa; they gather loyalists and a battle ensues with the Starks aided by the Knights of the Vale defeating the Bolton forces.
Split into simpler sentences: At the Wall, Melisandre resurrects Jon Snow, who is reunited with Sansa; they gather loyalists and a battle ensues. Aided by the Knights of the Vale, the Starks defeat the Bolton forces.