Pan-Germanism was highly influential in German politics in the 19th century during the unification of Germany when the German Empire was proclaimed as a nation-state in 1871 but without Austria (Kleindeutsche Lösung/Lesser Germany), and the first half of the 20th century in the Austro-Hungarian Empire and the German Empire. From the late 19th century, many Pan-Germanist thinkers, since 1891 organized in the Pan-German League, had adopted openly ethnocentric and racist ideologies, and ultimately gave rise to the foreign policy Heim ins Reich pursued by Nazi Germany under Austrian-born Adolf Hitler from 1938, one of the primary factors leading to the outbreak of World War II. As a result of the disaster of World War II, Pan-Germanism was mostly seen as a taboo ideology in the postwar period in both West and East Germany. Today, Pan-Germanism is mostly limited to some nationalist groups in Germany and Austria.
The word pan is a Greek word element meaning "all, every, whole, all-inclusive". The word "German" in this context derives from Latin "Germani" originally used by Julius Caesar referring to tribes or a single tribe in northeastern Gaul. In the Late Middle Ages it acquired a loose meaning referring to the speakers of Germanic languages (alongside 'Almain' and 'Teuton') most of whom spoke dialects ancestral to modern German. In English, "Pan-German" was first attested in 1892. In German there exists a synonym "Alldeutsche Bewegung" which is a calque using German instead of Latin and Greek roots.
Pan-Germanism's origins began with the birth of Romantic nationalism during the Napoleonic Wars, with Friedrich Ludwig Jahn and Ernst Moritz Arndt being early proponents. Germans, for the most part, had been a loose and disunited people since the Reformation, when the Holy Roman Empire was shattered into a patchwork of states following the end of the Thirty Years' War with the Peace of Westphalia.
Advocates of the Großdeutschland (Greater Germany) solution sought to unite all the German-speaking people in Europe, under leadership of the German Austrians from the Austrian Empire. Pan-Germanism was widespread among the revolutionaries of 1848, notably among Richard Wagner and the Brothers Grimm. Writers such as Friedrich List and Paul Anton Lagarde argued for German hegemony in Central and Eastern Europe, where German domination in some areas had begun as early as the 9th century AD with the Ostsiedlung, Germanic expansion into Slavic and Baltic lands. For the Pan-Germanists this movement was seen as a Drang nach Osten, in which Germans would be naturally inclined to seek Lebensraum by moving eastwards to reunite with the German minorities there.
The Deutschlandlied ("Song of Germany"), written in 1841 by Hoffmann von Fallersleben, in its first stanza defines Deutschland as reaching "From the Meuse to the Memel / From the Adige to the Belt", i.e. as including East Prussia and South Tyrol.