The birth of Poland as an independent nation coincides with the ascension of Mieszko I, in the year 960.
The major achievement of Mieszko was the adoption of the Christian faith under the authority of Rome - a fact which shaped Poland's history for the following centuries, and to this day.
Mieszko I died in A.D. 992. He was succeeded by his son, Boleslaw the Brave, who extended the boundaries of Poland and at the head of his army reached Kiev on the River Dnieper, later the capital of the Ukraine. He in turn was succeeded by his son Mieszko II, who reigned from 1025 to 1034. All these kings were members of the Dynasty of Piast, which continued its rule for several centuries.
The territory of the Poland of that time was quite similar to the present one, except that it did not include much of Silesia.
After several kings of the House of Piast, it produced its greatest monarch - Casimir the Great (1333-1378), who achieved during his long reign many changes and improvements throughout the country. Many splendid buildings - churches and castles - built under Casimir are still there. He allowed the Jews, expelled from other European countries, to settle in Poland and enjoy full freedom, including in religion and business.
Not all kings of Poland were Polish. There is nothing exceptional in that - after all, the present royal house of Britain is of German origin. King Louis (1370-1382) was a member of the French House of Anjou, founded by Saint Louis, but he was also king of Hungary, Poland, Dalmatia, Croatia, Rama, Serbia, Galicia, Lodomeria, Romania and Bulgaria. The vast empire of the Anjou dynasty did not promise to last long, as Louis had as yet no issue. Later he had two daughters: the princesses Elisabeth and Jadwiga, who became Queen of Poland in 1384.
Lithuania was at the time a major power. It extended over the territories now known as Bielorussia and Ukraine. It was in conflict with Poland and several battles were fought. The Polish senators, however, planned a masterpiece of statesmanship: a marriage of Grand Duke Jagiello with Queen Jadwiga. It would be a great sacrifice on her part, as the grand duke was three times her age and she was a beauty.
Jagiello was baptized in the Catholic faith and took the name of Wladyslaw. The Lithuanians were at the time pagans, worshipping snakes. Jagiello's brother Witold was also baptized. The union of Poland and Lithuania was not an annexation. Lithuania retained its identity and kept it for centuries, but the King of Poland was also Grand Duke of Lithuania.
The union of the two nations resulted in the largest power in Europe and remained in force for the following centuries. Some of the greatest men of Poland - such as the poet Mickiewicz in the 19th century and the national leader Pilsudski in the 20th - were of Lithuanian origin, but they did not know the Lithuanian language which, unlike Polish, is not a Slavonic language. The population of Lithuania was largely Ruthenian.
Jagiello proved to be a great statesman and became the founder of the Jagiellonian dynasty, which ruled the union for centuries.
Both Lithuania and Poland had been attacked by the Order of Teutonic Knights, a military order based in East Prussia. The German order was a major power which endeavored to extend its area eastward and south, and the Teutonic Knights were armed better than most European nations. Yet when the Teutonic Knights attacked in 1410, the united Polish and Lithuanian forces under the command of Jagiello defeated them in the great battle of Grunwald. Thus the Prussian efforts to conquer the entire Baltic coast and the northern provinces of the Polish-Lithuanian union were finished forever.
The last Jagiellonian king was Zygmunt-August (1548-1572). He was followed by Henri de Valois, a Frenchman. The next kings were Stefan Batory, a Hungarian, and Zygmunt Vasa, a Swede. The throne of the Polish-Lithuanian union was elective - a democratic feature unknown in other European countries. Foreign princes were elected largely because a Polish king might be considered as a favor for Poland and a Lithuanian one a favor for his country, while a foreigner was neutral.
Nevertheless, one of the best kings was Jan Sobieski (1674-1696), who saved Europe from a Turkish invasion. The Ottoman empire was then a major power. Its huge army besieged Vienna, which had it been seized it would have meant the victorious Turkish army would continue its invasion and thus place western Europe in mortal danger. Jan Sobieski, a great commander, saved Europe. His letters to his wife, a French princess, are a literary masterpiece.
The last king of the Union was Stanislaw Poniatowski (1764-1795).