And I've also read than he have made a ritual wich allowed him to take the soul of each man who die in the war.
And he old Naga Sadow power !
I have also read than he just wipped out the life of planet with just his little fingers..
But he want to doe the same to entire galaxy after the war have weaken the galaxy, and this will destroy the remanant of life, he also want the power to access to the ultimate immortality, because being immortal isn't enough !!!
DC members only destroy cities via rituals I believe.
__________________ "Vader's pulse and breathing were machine-regulated, so they could not quicken; but something in his chest became more electric around his meetings with the Emperor; he could not say how. A feeling of fullness, of power, of dark and demon mastery -- of secret lusts, unrestrained passion, wild submission -- all these things were in Vader's heart as he neared his Emperor. These things and more."