The Republic of Latvia is one of the nations in the Union of Königsberg, and is pretty much almost identical to OTL Latvia. It was formed from the southern remnants of the Duchy of Livonia by the Pskovians during their conquest of the Prussian Crown in the Continuation War of 1656-1658.
The Republic of Latvia is one of the first nations of the Union of Königsberg to be formed. The Territory that would become Latvia was conquered by the Teutonic Knights in the 1400s, and continued to be a part of the state after its reform into the Kingdom of Prussia in 14XX. The territory was under Prussian Dominion until 1594, when it rebelled to from the short-lived Duchy of Livonia until the conclusion of the Livonian War in 1614, when it reverted to Prussian control. This ushered in a new era of Peace that lasted until in 1649, the Pskovo-Narvan invasion of Prussia started the Lesser Northern War and began almost a decade of constant conflict for Prussia, until the Continuation War's conclusion in 1659. This series of conflicts, know to modern Historians as the Prussian Wars, saw the region of Livonia revolt after seven years of warfare with France and Rome, only to be aided in their rebellion with Pskov's declaration of war, citing a violation of the treaty of Reval's Free trade clause as casus belli (due to the Livonian Revolt). The Livonian rebels were aided by Pskov, who also set up the framework for what would become the Republic of Taalin, and the Republic of Latvia. While the Republic of Taalin would unify with Narva to form the Federal Republic of Eesti shortly after its formation, Latvia remained Independent.