Short answers, pulled from the story.
Mieszko I of Poland accepted Christianity in 966 to establish the first independent Polish state. This decision placed a nucleus between the Oder and Vistula rivers on the North-Central European Plain into the broader Christian world.
In February 1772, an agreement for the partition of the Polish, Lithuanian Commonwealth was signed in Vienna, causing Poland to lose about 30% of its territory. On the 24th of October 1795, representatives of partitioning powers signed a treaty dividing the remaining territories until the independent Polish state disappeared from maps entirely.
Poland lost over 20% of its pre-war borders when territories east of the Curzon Line were permanently annexed by the Soviet Union. Poland received former German territory east of the Oder, Neisse line which included southern two thirds of East Prussia and most of Pomerania.
On the 11th of November 1918, Poland proclaimed independence after liberating parts of southern and central Poland. Cities like Tarnów and Kraków were liberated on October 31, reaching Warsaw on November 11.
On the 20th of May 1945, an agreement for return to 1938 borders was signed in Trstena between Czechoslovakia and Poland. Agreement concerning final demarcation of state frontier between Czechoslovakia and Poland signed the 13th of June 1958 confirmed border at line of the 1st of January 1938.