matthewdenn wrote:although I will concede that I think that East Prussia should go back to Germany instead of this little hunk in Russian hands.
Northern part of East Prussia (the part which belongs to Russia today) was never inhabited by any significant amounts of either Russians or Poles. But southern part of East Prussia (so called Mazury in Polish) was ethnically Polish since the Middle Ages.
The main reason why southern part of East Prussia voted for Germany in 1920 was the fact that at the time when the plebiscite was carried out, the state of Poland was in an extremely dangerous and critical political and military situation. Bolshevik armies were quickly approaching Warsaw and it was generally thought that Poland stood no chance for repulsing the Bolshevik invasion and remaining days of Poland were already counted, it would fell very soon. Another factor which had got significant influence on the result of this plebiscite (carried out on 11.07.1920) was terror and persecutions of ethnic Poles - especially influential Polish political activists - organized and carried out by German authorities in East Prussia.
The history of Polish colonization of Prussia goes back to the times of 13th century. Ethnic Poles started to settle in Prussia when armies of the state of the Teutonic Order supported by dukes of Poland and various crusaders and mercenaries from all around Europe conquered and captured territories of pagan Prussian tribes. This ethnic Polish colonization of Prussia became even more intensive during the following centuries - 14th and 15th - and lasted as long as until the end of 17th century.
Social and regional composition of Polish colonists who settled in former pagan Prussian territories then held by the state of the Teutonic Order was varied. Major part of these colonists were peasants and not very well-off knighthood and nobility - usually owners of only a part of a village up to one entire village. There were also some townsmen, mainly members of the plebs social class, artisans and also minor merchants. Seldom patricians. They were coming to Prussia in order to search for better live conditions, new uninhabited lands or in order to make a fortune and also induced by Teutonic authorities. That's why they were mainly coming from the historical region of Mazovia - which at that time (13th - 15th centuries) was the most underdeveloped part of Poland - completely different than developed and reach provinces of Silesia, western part of Lesser Poland (so called Land of Cracow), Greater Poland and Cuiavia.
Since late 13th century until middle 14th century Mazovia was often considered as a separated and independent from Poland - but ruled by Polish dukes from Piast dynasty - state, although the process of gaining independence from Poland by Mazovia was not immediate, but long and gradual and strictly connected with the progressing phenomenon of feudal fragmentation in Poland (power and position in the state of the senioral duke / princeps was slowly becoming smaller and smaller, and some dukes were not recognizing the rule and superiority of senioral dukes from Cracow any more). Mazovia even became a faithful ally of the Teutonic Order during its wars against the Kingdom of Poland fought in 14th century, and also was temporarily subordinated to the Bohemian king as his vassal during that century.
As was written above, ethnic Poles who settled in Prussia in the Middle Ages mainly came from Mazovia. That's why they were called "Mazurzy" = "the Mazurs" or "the Mazurians" (because inhabitants of Mazovia are called Mazowszanie or Mazurzy) and the Polish name for this region (which was used for the first time in early 19th century) is "Mazury".
Ethnic Poles mainly settled in the southern part of Prussia. The northern border of the compact Polish colonization in this province was - more or less - along the line Morag - southern Warmia (German: Ermland) - Ketrzyn - Wegorzewo - Gołdapia (Goldap). Teutonic (later German) administration was calling these lands "die polnischen Ämter"
Map from the excellent book "Państwo Zakonu krzyżackiego w Prusach. Władza i Społeczeństwo" ("The state of the Teutonic Order in Prussia. The authorities and the society"), PWN, Warsaw, 2008 - page 207:
"Map 11. Directions of colonization of the state of the Teutonic Order in 13th and 14th centuries."
Black arrows - German colonization
White arrows - Polish colonization
Dark areas - property of bishops (mainly in Warmia = Ermland)
The Mazurs - unlike native Prussians - did not undergo Germanization (vast majority of native Prussians were Germanized until the end of 17th century) and retained their Polish language and customs. But they did not retain Catholic religion - vast majority of all Mazurs were Lutherans in 19th century. Due to progressing German pressure and persecution of Poles in East Prussia in 19th century - especially during the times of Bismarck and his "Kulturkampf" - Mazurzy tried to defend and protect their distinguishing characteristic - at first as regional community, later also as part of the Polish nation. Since 1842 Polish newspapers were being published in East Prussia - like for example "Przyjaciel Ludu Łecki" or "Mazur". At the end of 19th century Polish political activists concentrated mainly around "Gazeta Ludowa" newspaper and Mazurska Partia Ludowa (MPL) political party. In 1910 Mazurski Bank Ludowy bank was founded. After the First World War Mazurski Komitet Plebiscytowy and Mazurski Związek Ludowy were managing the action of incorporating Mazury (so southern part of East Prussia) to the state of Poland.
In the interwar era many Polish organizations existed in Mazury. For example between 1923 and 1928 - Zjednoczenie Mazurskie (The Mazurian Federation) with head office in the town of Szczytno. Many Mazurian activists were members of the Związek Polaków w Prusach Wschodnich (Association of Poles in East Prussia) and together with members of this association joined the Związek Polaków w Niemczech (Association of Poles in Germany) in 1922.
Persecutions of Polish activists intensified in years 1928 - 1932 and after Hitler came to power. During the Second World War many Mazurians were imprisoned or murdered by the Nazis in prisons or concentration camps.
Mazury were captured by the Red Army in January and February of 1945 and incorporated by Joseph Stalin to the People's Republic of Poland. But new communist authorities were treating Mazurians almost as bad as Germans and Volksdeutche, and as the result of this policy many of them departed from Polish national identity and Polish customs, or decided to emigrate / escape to the United States of America.
After escape / expulsion of Germans and emigration of many Mazurians to the USA, Mazury and especially other parts of former East Prussia were mainly populated by Polish repatriates expulsed from pre-war Polish territories in Eastern Poland - especially from the Wileńszczyzna region with the city of Wilno (today part of Lithuania).