When Hoffmann von Fallersleben wrote his 1841 poem "Deutschland ueber alles" which eventually became the German national anthem in the 1920s, the first verse spelled out the geographic boundaries of his national audience, "von der Maas bis an die Memel", two rivers at the western and eastern ends.
When Germany lost World War I, the Treaty of Versailles stripped away a small chunk of land along the Memel river and gave it eventually to be ruled as part of Lithuania. As Hitler re-armed and began to assert claims to German populated territories, Memel became an obvious and tempting target. Only days after destroying Czechoslovakia and imposing a Reichs Protectorate over Bohemia-Moravia, his Foreign Minister von Ribbentrop invited the Lithuanian Foreign Minister to Berlin and presented him with what was essentially an ultimatum: turn over the Memel-Land (Lithuania's only sea port) to Germany. Finding no support from the allies, Lithuania had no choice but to yield.