After World War I the entirely ethnic German Neumark remained within the Free State of Prussia, itself part of the Weimar Republic (Germany).

After World War II the Potsdam Conference assigned the majority of the Neumark to Polish administration, and since 1945 has remained part of Poland.

[citation needed] After AD 500 West Slavic tribes gradually repopulated the area, which became a forest borderland between Pomerania and Greater Poland.

[1] Polish rulers incorporated the future Neumark territory as the Lubusz Land and by the beginning of the 13th century the previously depopulated region had a thinly-spread population of Poles.

Beginning in the 1230s, Low-German–speaking colonists from the Holy Roman Empire began settling north and south of the Warta and Noteć Rivers upon the initiative of Pomeranian and Polish lords (see Ostsiedlung).

The Ascanian margraves of Brandenburg, starting with Albert the Bear (ruled 1157–1170), aspired to extend their dominion east of the Oder.

For instance, the Polish castellany of Santok, an important base and crossing point over the Warta near its junction with the Noteć, was sought by Pomerania.

To relieve himself of the trouble of maintaining the fortress, Duke Przemysł I of Greater Poland granted the castellany to Margrave Conrad as a dowry for his daughter Konstancja.

Unlike in the rest of Brandenburg (where the Ascanians settled knights in open villages) the margraves began constructing castles in their land east of the Oder to guard against Poland.

Because the new Terra trans Oderam, or "land across the Oder", formed an extension of the Margraviate of Brandenburg, it became known as the Neumark ("New March") after the middle of the 15th century.

After the Teutonic Knights' defeat in the Battle of Grunwald (Tannenberg) in 1410, the future Grand Master Michael Küchmeister von Sternberg used the Neumark as a staging ground for an army of German and Hungarian mercenaries which he later used against the forces of King Władysław II Jagiełło of Poland.

An enthusiastic supporter of the Protestant Reformation, John succeeded in converting the Neumark to Lutheranism and in confiscating church property.

The division of Brandenburg resulted in trade wars between the brothers, as Crossen and Landsberg competed with the Kurmark's Frankfurt for mercantile primacy.

With the death of both brothers within ten days of each other in 1571, the Neumark became reunited with the Kurmark under Joachim II's son, John George.

During the Thirty Years' War (1618–1648) both Swedish and Imperial troops plundered, ravaged and burnt the land, while plague epidemics in 1626 and 1631 killed much of the populace.

In the Weimar Republic's National Assembly of 1 November 1919, the majority of the region voted for the Social Democratic Party of Germany (SPD).

With the construction of modern roadways, of the Fernverkehrstraße 1 (an arterial road from Berlin to Königsberg), and of the Prussian Eastern Railway, the Neumark also began to develop industrially.

Such development was primarily geared toward agricultural needs and was concentrated near the cities of Landsberg and Küstrin, and the Neumark did not become nearly as industrialized or densely populated as other German areas such as the Ruhr, Saxony, or Upper Silesia.

Because the Red Army had advanced so quickly, the civilian population of the region suffered greatly from warfare and occupying troops because they had not prepared to flee in time.

A small part of the German population, mostly technicians for the water supply companies, were retained and used for compulsory labour; they were allowed to emigrate to Germany in the 1950s.