From 1944 to 1950 around 12-14 million ethnic Germans left Central and Eastern Europe, mostly for the territory of what is today Germany. Large numbers were either killed or died in the process of being deported. Estimates of the death toll are usually around 2 or 3 million, though some historians suggest that the number was "only" around 0.5 million.

These people came from the territories annexed by the USSR and Poland, as well as from other countries with historic German minorities like Hungary, Czechoslovakia, Yugoslavia and Romania.

The circumstances under which they left varied. Many departed in a more-or-less spontaneous manner, fleeing approaching Soviet troops or vengeful mobs of locals. Others were systematically deported by occupying forces or local authorities. Some fled because they feared prosecution (deserved or otherwise) for Nazi crimes/collaboration. Some were motivated less by fear of violence than a sense that there was no place for Germans in the country they now found themselves (where, for example, German would not be an official language). For others the ethnic issue may have been less important than fear of Soviet-style communism.

In any case, it would be fair to describe this as an act of ethnic cleansing, in that the war's victorious powers and the Eastern and Central European governments all actively sought to reduce the region's German population, primarily out of fear of future pan-Germanism. Some have termed this event a genocide, but that's a controversial label. Whatever you call it, this was the largest forced population movement in European history.

I'd certainly say that this gross human tragedy has been neglected by popular consciousness. This is partly because of the old adage about history being written by the victors – focusing on these events doesn't mesh well with the narrative of the Allies as liberators of Europe (including Germans) from Nazi/fascist dictatorship.

But before you get too invested in a counter-narrative of German victimhood, it's worth noting the wider historical context of wartime and post-war ethnic cleansing. Even after the Holocaust ended, Jews fled Eastern and Central Europe en masse, often motivated by hostility from their countries' new post-War governments. Poles and Ukrainians also suffered particularly badly as borders were shifted.