After the war

It was two months after The Battle of Hogwarts. Many had lost their lives. Families were torn apart. The wizarding world was in mourning. But. Suddenly, as if the very forces of life and death had heard the unsaid plea, people were coming back.
Back. To. Life.
Every member of the light side who had been murdered by Voldemort and his army of Death Eaters were coming back.
Wasn't it known that no spell can reawaken the dead?
Then how?
How were people long dead walking the Earth very much alive? Was it a gift ?
A gift for finally ridding the Wizarding World of Voldemort?
Or was it because a certain someone was the Master of Death?