This is a line between lands. 
This line is a border. 
The Oder–Neisse line is a border. 

This border changed after World War II. Before the war, the border was in a different place. At the Potsdam Conference, leaders decided to move it. This move gave more land to Poland. Large areas like Silesia and Pomerania went to Poland. Other parts went to the Soviet Union.
Many people had to move because of these changes. About 12 million German people lived in these lands in 1944. They fled as the Soviet Red Army moved forward.
For a long time, leaders argued about the line. East Germany and Poland agreed to it in 1950. West Germany did not agree right away. Later, in 1972, West Germany signed a treaty about it. Finally, in 1990, a new treaty made it official.
The Oder–Neisse line is the modern border between Germany and Poland. 

This border was created through big changes after World War II. At the Potsdam Conference, leaders decided to shift Poland's borders westward. This meant giving certain lands to Poland and others to the Soviet Union. Large areas like Silesia and Pomerania became part of Poland. The southern part of East Prussia also went to Poland. However, the northern part of East Prussia went to the Soviet Union. This area included the city of Königsberg, which was renamed Kaliningrad.
History shows that these lands have belonged to different groups for a long time. In the 10th to 13th centuries, the lower Oder was a border for Piast Poland. Later, many people lived in these areas with different cultures. In parts of Pomerania, Slavic cultures and languages stayed strong for a long time. 
The move of the border caused many people to leave their homes. In the autumn of 1944, an estimated 12 million German people lived in these territories. Many of them fled as the Soviet Red Army moved forward. 
It took many years for everyone to agree on this line. From 1950 to 1990, the line was the border for East Germany and Poland. 

The Oder–Neisse line is the term used for the modern border between Germany and Poland. 

The creation of this line involved a complex process of territorial exchange. During the Potsdam Conference, leaders decided to shift Poland's borders westward. This meant that large areas of land were transferred to new countries. Nearly one quarter, or 23.8 percent, of the Weimar Republic's land area was ceded. This area was part of Germany before the war. Most of these territories, such as Silesia and Pomerania, were given to Poland. The southern part of East Prussia was also transferred to Poland. However, the northern part of East Prussia went to the Soviet Union. This area included the city of Königsberg, which was renamed Kaliningrad.
Historical records show that these lands have seen many different rulers. From the 10th to the 13th century, the lower Oder served as the western border for Piast Poland. 
The shift in borders happened during a very difficult time in history. In the autumn of 1944, an estimated 12 million German people lived in these territories. Many of them fled as the Soviet Red Army advanced through the region. 
Before the current border was set, there were many different proposals for where the line should be. After World War I, the Treaty of Versailles fixed the border between Poland and Germany. This border was adjusted to reflect the ethnic groups living in small areas. In some places, like Upper Silesia, a plebiscite was held to let people vote on which country they preferred. This vote involved over 1.1 million people. However, the process was marked by severe ethnic tensions and protests. In the city of Danzig, which was 90% German and 10% Polish in 1919, a compromise was made. The city became a "Free City" with special rights for Poland.
It took several decades for the Oder–Neisse line to be fully accepted by all neighbors. From 1950 to 1990, the line served as the border between East Germany and Poland. 

The Oder–Neisse line is more than just a line on a map. It is a connection to the complex history of Central Europe. It connects the natural geography of rivers and seas to the political decisions of world leaders. The line shows how borders can change due to war, negotiations, and shifting populations. Understanding this border helps us understand the modern relationship between Germany and Poland. It serves as a permanent marker of how the map of Europe was reshaped in the 20th century.
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