The Republic of Belarus (formerly Byelorussia) is a landlocked country in eastern Europe, bordering Russia, Latvia, Lithuania, Poland and Ukraine. Its language and people are very close to Russia's, so much that the very same idea of a separate Belarussian nationality did not become popular until the 20th century. The name Belarus even means White Russia. It was first organized as a separate state in 1919 and in 1922 became one of the founder republics of the Soviet Union, of which Belarus would remain part of until the former's dissolution in 1991. Its western half was occupied by Poland between the Polish-Soviet War and World War II.
Belarus is notable today for being the last remaining authoritarian state in Europe and the country where the Soviet legacy is most present and visible. Its economy is controlled by the state and even the secret service still goes by the name KGB.
In most of Turtledove's works, Belarus is either part of the Soviet Union, or does not exist at all.
During the first days of the Second World War in October 1938, the People's Republic of Byelorussia gained strategic importance due to its nature as the Soviet Union's closest point to Germany. Soviet airplanes flew out of Byelorussia regularly to bomb East Prussia. The task was risky, however, since both territories were separated by lands conquered by Poland in the Polish-Soviet War of the 1920s.
The existence of a large Byelorussian community in these lands, which the Soviet government claimed was discriminated against by the Poles, provided Joseph Stalin with a casus belli against Poland in the very last days of 1938. In response, the Polish government forged an alliance with Germany, which was committed to the invasion of France. The USSR's initial invasion at the heart of winter, however, was a complete disaster. The Polish resisted successfully and their air force bombed some Soviet cities, including Byelorussia's capital, Minsk. The Soviets answered then by launching a full-on invasion of the whole of Poland in 1939.