The theater of Polish history is the vast plain extending from the Carpathians to the Duena, and from the Baltic almost to the Black Sea and the Sea of Azov.

This region, lacking natural frontiers on several sides, was inhabited by a variety of races: Poles in the west, Lithuanians in the east, Ruthenians in the south and many Germans in the cities.

The union of the Polish and Lithuanian states was as yet a merely personal one in the monarch.

Since the fourteenth century the crown of Poland had been elective, but the grand-ducal crown of Lithuania was {139} hereditary in the famous house of Jagiello, and the advantages of union induced the Polish nobility regularly to elect the heir to the eastern domain their king.

Though theoretically absolute, in practice the king had been limited by the power of the nobles and gentry, and this limitation was given a constitutional sanction in the law _Nihil novi_, [Sidenote: 1505] forbidding the monarch to pass laws without the consent of the deputies of the magnates and lesser nobles.
The foreign policy of Sigismund I [Sidenote: Sigismund I, 1506-1548] was determined by the proximity of powerful and generally hostile neighbors.