Why did uncle have a impact on Salvas life ?

Salva's Uncle gave Salva some comfort and protection. Jewiir used to be a member in the Sudanese army and he stumbled upon the group fleeing Sudan. In that group, he found Salva and then he decided to escort the group to Ethiopia and then return back home to fight for his country. Unfortunately, Jewiir was killed shortly before entering Ethiopia and Salva remained alone once more.