The Federated Commonwealth features in the fictional Battletech universe.
The union of the Lyran Commonwealth and the Federated Suns in 3030. Led by First Prince Hanse Davion and his wife Archon Melissa Steiner-Davion. Later led by Archon-Prince Victor Ian Steiner-Davion, and usurped by Archon-Princess Katherine Steiner-Davion. In 3067 the great state was sundered once and for all, back into the Lyran Alliance (Commonwealth) and the Federated Suns. The Lyran district is led by Archon Peter Steiner-Davion, and the FedSuns led by Regent Yvonne Steiner-Davion and her husband Duke Robinson, Tancred Sandoval.
(Note: The Corps of Federated Commonwealth Regimental Combat Teams have splintered into two groups for the Lyrans the new Alliance Guards, and for the Suns the FedSuns Lancers.)