Poland's unlikely partnership with the adjoining Grand Duchy of Lithuania, Europe's last heathen state, provided an immediate remedy to the political and military dilemma caused by the end of the Piast Dynasty. At the end of the fourteenth century, Lithuania was a warlike political unit with dominion over enormous stretches of present-day Belarus and Ukraine. Putting aside their previous hostility, Poland and Lithuania saw that they shared common enemies, most notably the Teutonic Knights this situation was the direct incentive for the Union of Krewo in 1385. The compact hinged on the marriage of the Polish queen Jadwiga to Jagiello, who became king of Poland under the name Wladyslaw Jagiello. In return, the new monarch accepted baptism in the name of his people, agreed to confederate Lithuania with Poland, and took the name Wladyslaw II. In 1387 the bishopric of Wilno was established to convert Wladyslaw's subjects to Roman Catholicism. (Eastern Orthodoxy predominated in some parts of Lithuania.) From a military standpoint, Poland received protection from the Mongols and Tatars, while Lithuania received aid in its long struggle against the Teutonic Knights.

The Polish-Lithuanian alliance exerted a profound influence on the history of Eastern Europe (see fig. 3). Poland and Lithuania would maintain joint statehood for more than 400 years, and over the first three centuries of that span the "Commonwealth of Two Nations" ranked as one of the leading powers of the continent.

The association produced prompt benefits in 1410 when the forces of Poland-Lithuania defeated the Teutonic Knights in battle at Grunwald (Tannenberg), at last seizing the upper hand in the long struggle with the renegade crusaders. The new Polish Lithuanian dynasty, called "Jagiellon" after its founder, continued to augment its holdings during the following decades. By the end of the fifteenth century, representatives of the Jagiellons reigned in Bohemia and Hungary as well as PolandLithuania , establishing the government of their clan over virtually all of Eastern Europe and Central Europe. This farflung federation collapsed in 1526 when armies of the Ottoman Empire (see Glossary) won a crushing victory at the Battle of Mohács (Hungary), wresting Bohemia and Hungary from the Jagiellons and installing the Turks as a menacing presence in the heart of Europe.

Data as of October 1992