Masuria and the Masurian Lakes Plateau are known in Polish as the Kraina Tysiąca Jezior, and in German as the Land der Tausend Seen which means the same: "land of a thousand lakes". As in other parts of northern Poland, from Pomerania on the Odra river to the Vistula (Wisła) river, one continuous stretch of lakes makes it a beautiful holiday location. These lakes were ground out of the land by glaciers during the Ice Age, when ice covered north-eastern Europe. By 10,000 BC this ice started to melt. Great geological changes took place and even in the last 500 years the maps showing the lagoons and peninsulas on the Baltic Sea have greatly altered in appearance.
In the southern part of the region, the ancient Sudovia and Galindia lands, wilderness areas survived for longer than in most of Europe. The deep forests in these territories made it possible for moose, aurochs, bears and many other mammals to survive. During the Baltic or Northern Crusades of the 13th century the native Prussian population also had the chance to survive in the remaining wilderness areas against the onslaught of the Teutonic Knights (of German origin) and other crusaders from elsewhere in Europe (mainly from Germany), who sought conquest of the land and conversion of the native population to Christianity. The southern parts of the region were already largely penetrated by Polish settlements.
Polish settlers, mainly from Masovia, so called Mazur, began to arrive following the Teutonic Order's conquest of the area. German, French, Flemish, Danish and Norwegian colonists entered the area shortly afterward, founding numerous cities and towns. The original Prussian population was almost completely exterminated, by the 15th century. Lucky survivors of the pogrom were forcefully Germanized or Polonized, depending on majority in the local area. In 1466 Teutonic Order acknowledged the overlordship of the Polish crown. Since 1525 Masuria (with the exception of Warmia) has had a mostly Protestant population. The cities remained centres of German and Polish speakers, while the old Prussian language survived in parts of the countryside until the early 18th century.
In 1656 the Ducal part of Masuria was devastated during the Deluge, when it was raided by Tartars and Poles as retaliation for the betrayal of the Prussian prince. In 1708 some one third of population died during the Plague. Losses in population were again compensated by migration from Poland and refugees from all over the world, including Polish Arians (Polish Brethren), expelled from Poland in 1657. The last such group were the Russian Filipons in 1830.
Germanisation was slowly and mainly done by education: in 1872 Polish language was removed from schools. In 1890 143,397 of Masurians gave German as their language (either first or second), 152,186 Polish, and 94,961 Masurian. In 1910, the German language was given by 197,060, Polish by 30,121, and Masurian by 171,413. In 1925, only 40,869 people gave Masurian as their native tongue and only 2,297 gave Polish.
The name Masuria began to be used officially after new administrative reforms in Prussia after 1818.
The League of Nations held a plebiscite in 1920 as to whether the people of the two southern districts of East Prussia wanted to remain within Prussia or to join the state of Poland: 97.5% voted to remain with Prussia. The factors, which might influence the effects are both using the "Prussia" instead of "Germany" (since large chunk of population did not consider themselves neither "Germans" or "Poles", and "Prussia" was name close to them as name of their "little fatherland") - mainly because status of post-war Germany was unclear - and that during the plebiscite, the currently advancing Soviet Army was on the Vistula line, they had a peace pact with Germany, and they were ready to invade any territories that would pass to Poland as a result of the plebiscite. There is possibility that the motivation for people to vote the way they voted, was to keep the Soviet hordes, known for brutality, away from their homes. The effect surpised local Polish National organizations, because they were the strongest in Masuria, even stronger than in Silesia.
Partly devastated by war between the retreating German and advancing Soviet armies in 1944 - 1945, Masuria was placed under Polish administration as a result of the Potsdam Conference following Germany's surrender in 1945. Even before most of the German population fled to Germany and elsewhere, and was replaced by Poles expelled from the territories taken over by Soviet Union in 1939. In 1999 Masuria was reconstituted with neighbouring Warmia as a single administrative province through the creation of the Warminsko-Mazurskie voivodship.