Analysis of information sources in references of the Wikipedia article "Territorial evolution of Poland" in English language version.
Established as a kingdom in 922 under Mieszko I, Poland was united with Lithuania in 1386 under the Jagiellon dynasty (1386–1572) to become the dominant power in east-central Europe, enjoying a prosperous golden age.
Formally, Poland and Lithuania were to be distinct, equal components of the federation... But Poland, which retained possession of the Lithuanian lands it had seized, had greater representation in the Diet and became the dominant partner.
(Sept. 19, 1657), agreement in which John Casimir, king of Poland from 1648 to 1668, renounced the suzerainty of the Polish crown over ducal Prussia and made Frederick William, who was the duke of Prussia as well as the elector of Brandenburg (1640–88), the duchy's sovereign ruler.
Zasadniczym i podstawowym powodem powyższej decyzji zapisanej w artykule 28 traktatu była konieczność włączenia do Polski obszaru linii kolejowej łączącej Gdańsk z Warszawą. – Translation – The primary and fundamental reason for this decision, enshrined in article 28 of the Treaty, was the need to integrate the Polish area of the railway line connecting Gdańsk and Warsaw.
A Western Ukrainian People's Republic was also declared in Lviv on October 19, 1918. The ZUNR formally (and largely symbolically) joined the UNR
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ignored (help)At its apogee, the Polish–Lithuanian Commonwealth comprised some 400,000 square miles (1,000,000 km2) and a multi-ethnic population of 11 million.
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