"The Prince of Nothing" trilogy by R. Scott Bakker
The Darkness That Comes Before (2004)
The Warrior-Prophet (2005)
The Thousandfold Thought (2006)
It's "dark fantasy"
From wiki: "The Prince of Nothing trilogy was published between 2003 and 2006. It depicts the story of the Holy War launched by the Inrithi kingdoms against the heathen Fanim of the south to recover the holy city of Shimeh for the faithful. During the war, a man named Anasûrimbor Kellhus emerges from obscurity to become an exceptionally powerful and influential figure, and it is discovered that the Consult, an alliance of forces united in their worship of the legendary No-God, a nihilistic force of destruction, are manipulating events to pave the way for the No-God's return to the mortal world."