1000 years of Polish history commenced when a political move brought Poland into being. In 965, an ambitious and insightful Slavic leader Mieszko I married a Bohemian princess and converted to Christianity in order to counter the growing strength of his German neighbors to the west.
By inviting the Holy Roman Empire into the region the following year, Mieszko established the Piast dynasty and ensured a separate identity for the lands that soon came to be known as Poland. That diplomatic gain brought political and economic ones as well: Poles mimicked the Church administration, and quickly put to use the new ideas and technology that now flowed in from the west.
With one baptizing stroke, Poland took a position which it would hold for centuries: as a buffer zone between the West and the East, its fortunes would rise and fall in a manner unique in European history.
Following its befitting beginning with the blessing of Christianity, Poland soon exhibited another national trait: the individual is king.
In 1138, Poland was parceled out among several Piast sons, fragmenting it geographically and politically. As could be expected, the brothers began to fight among themselves, leaving Poland incapable of fighting off outsiders. The state grew weaker and weaker over the next 200 years, losing the Pomeranian region to the north and yielding to the more subtle threat of a germanized Silesia.
To counter these losses, Poland invited the Teutonic Knights in to protect its eastern and northern flank. The Knights accepted, set up shop throughout the north, and eventually grew into a threat of their own. In 1308, they took Gdansk, renamed it Danzig, and built it into a thriving trade center. By settling Germans in the area, the Teutonic Order precipitated a tug-of-war over the region which lasted until 1945.
Cut off from the sea, fragmented, growing weaker each year, it was not until the early part of the 14th century that the tide turned when Wladyslaw I and his son Kazimierz III reunified and reformed Poland.
Kazimierz III in particular altered Poland, from the ground up.
He codified the laws, he reformed the administration, he organized provincial governments, he established Jagiellonian University - one of the first in Europe, and he welcomed the pogrom-plagued Jews from the west. As the old saying goes, Kazimierz "received Poland of wood and left it of stone".