Aldred was crowned Emperor. With the support of the entire Empire, his rule was unchallenged. The nobles did not form a group against him because they were completely loyal under the Empress, and since the Empress herself chose Aldred as Emperor, it meant that he was one of them.
With the Empire in complete unity, they could defend themselves against any outside threat.
It was amazing what Aldred and Edeline manage to do. Edeline's decades long planning, Aldred's overwhelming strength.
These two factors let them take a quick swoop and took over an entire Empire. Nobody had ever seen something like this before.
Usually, when someone forcefully took over an Empire, a lot of people would be angered and riots and protest would fill every corner of the nation. Even if those riots were to be destroyed and eliminated, secrets and hidden enemies would make the ruler wary on who to trust.
Sooner or later the nation would crumble from inside.