In his book, The famous American historian, Yale professor Timothy Snyder explores the phenomenon of the birth of modern nations. The book begins with a review of the creation in the XVI century of the Polish – Lithuanian Commonwealth-the largest state of early modern Europe. At the end of the twentieth century, when this study ends, the lands of the former Polish-Lithuanian Commonwealth were divided among themselves by states named after nations: Poland, Ukraine, Lithuania and Belarus. According to the most common idea of nationality at that time, state borders were supposed to cover Linguistic Communities. How did four modern ideas arise from one early modern national idea? The author's answer is intended to attract the attention of both professional historians and people who care about issues of their own identity.