Even though he is from Shurima, his ties to his homecountry are very weak, due to his preoccupation with the void.
Kassadin is on a mission to avenge his daughter Kai'Sa and his wife, who were taken by the Void 10 years in the past, his mission also includes stop the Void from spreading across Runeterra and to keep the veil separating both planes from shattering completely.
Kassadin and Malzahar are polar opposites. While Kassadin tries to fight the void, Malzahar tries to bring it to Runeterra.
In the new lore, Kassadin blamed Malzahar for open the Void rift that killed his wife and daugther .