During the New Kingdom there occurred a revolution within the art community as well as a political upheaval. Akhenaton briefly c
hanged the course of religious activity when he worshipped only one god, Aton. He closed the all temples not dedicated to Aton, and he eliminated the very powerful priesthood of Amen. In brief, how did he abolish the power of the priesthood?
He decided that now the Pharaoh was the only one who could speak with gods (or god, in this case), and there was no need of priesthoods anymore.
Explanation:
Now, let's understand. Until this reform, the priesthoods had more power than the Pharaoh because they were responsible to communicate gods' will to the mortals. Because of this importance, their wealth and influence were huge, creating several controversies and conflicts, sometimes. When Akhenaten decides that there is just one god and he, the Pharaoh, is the only one who can get in touch with this deity, he establishes that the priesthoods are no longer necessaries. Of course that this reform was not promoted without resistance, so in many cases, he had to use the force and sentenced to death anyone who didn't accept this change.
