The Republic of Sidemore was an independent star nation in the Marsh System on the edge of the Silesian Confederacy.
The capital of the Republic was Sidemore, the sole habitable planet of Marsh. (HH6)
In recognition of Captain Honor Harrington's contribution to restoring their freedom following the occupation of Sidemore and Marsh by Andre Warnecke and his fugitive followers, the Sidemorians maintained a treaty relationship with the Star Kingdom of Manticore, and later began expanding their trade into Silesia. (HH6, HH10)
The Republic's armed space forces were called the Sidemore Navy. (HH10)
In 1920 PD, following the partitioning and annexation of Silesia by the Andermani Empire and the Star Kingdom, the Republic remained an independent star nation and ally of the Star Empire of Manticore. (infodump, Companion)