Cover art by Richard Anderson.

Empire Ascendant is the second book in the Worldbreaker Saga trilogy.  It was first released in the UK on 1 October 2015 and in the US on 6 Oct 2015.  It picks up directly after the events of Mirror Empire.  Like Mirror Empire, it features cover art by Richard Anderson and was published by Angry Robot Books.  

Synposis from the back of the book:

Every two thousand years, parallel dimensions collide on the world called Raisa, bringing a tide of death and destruction to all worlds but one. Multiple worlds battle their dopplegangers for dominance, and those who survive must contend with friends and enemies newly imbued with violent powers.

Now the pacifist country of Dhai's only hope for survival lies in the hands of an illegitimate ruler and a scullery maid with a powerful – but unpredictable –magic. As their dopplegangers spread across the world like a disease, a former ally takes up her Empress’s sword again to unseat her, and two enslaved scholars begin a treacherous journey home with a long-lost secret that they hope is the key to the other worlds' undoing.