The Fist of the Empire, alternatively known as the Sith Army, represented the Sith organization conceived by Sith Lord Darth Tyranus. His intention was to establish this army after his master's New Order, also known as the Galactic Empire, was brought into being at the conclusion of the Clone Wars.
Darth Tyranus, who was also known as Count Dooku, envisioned the Fist as a group formed from what remained of the Jedi Order. Those Jedi who refused to embrace the dark side of the Force were to be killed, while those who yielded would be indoctrinated into the ways of the Sith. Anakin Skywalker was to be the central figure, using his influence and access to the HoloNet to subtly criticize the Jedi Order, blaming them for the war's extended length, and eventually announcing the creation of a new group of Force users. Dooku imagined Skywalker as a leading general in the Fist after the New Order was established.
The Fist was intended to impose its will through strength, in contrast to the Jedi's well-known diplomatic approach. Only Humans (and seemingly near-Humans) would be allowed to join the Fist. All Force-sensitive Humans throughout the galaxy would be conscripted into the Fist as children, regardless of their or their parents' desires, and they would be trained in the Sith ways. Dooku's plans suggested that Force-sensitive sub-species like the Korunnai, Kiffars, and Dathomiri would be fully integrated into the Fist.
The extent to which Palpatine agreed with this plan is uncertain, and it may have been a manipulation of Dooku's own beliefs and ambitions. While Palpatine did create the Inquisitorius, his Dark Side Elite, and the Emperor's Hands, very few of their members were former Jedi, even fewer were trained in Sith practices, non-humans were included in their ranks, and there is no evidence that Force-sensitive subspecies were enslaved by it. Ultimately, this concept was abandoned aboard the Invisible Hand when Skywalker decapitated Dooku.