Lithuania is one of the three small Baltic republics, a.k.a the Baltic States.
Most Lithuanians belong to the small ethno-linguistic group of Balts, which also includes modern Latvians. (Proto-Balts and proto-Slavs shared common ancestry and this has led to both language families sounding the closest to each other of all the Indoeuropean languages present in Europe.) Lithuania was among the last bigger countries in Europe to adopt Christianity, in the 14th century. During much of the early modern era, Lithuania coexisted in personal union with Poland and formed the Polish-Lithuanian Commonwealth, an OTL state that is often praised as well as joked about on AH.com.