Answer:
6000 years ago
We believe Sumerian civilization first took form in southern Mesopotamia around 4000 BCE—or 6000 years ago—which would make it the first urban civilization in the region. Mesopotamians are noted for developing one of the first written scripts around 3000 BCE: wedge-shaped marks pressed into clay tablets.
The mongols invaded china with the intentions of having china under the Mongol Yuan rule.
They knew the land,and had the homefield advantage.
East Berlin, the capital of the new communist regime of Eastern Germany was not happy with the fact that West Berlin was occupied by the US, Britain and France. This area was the only one behind the Iron Curtain that the Western powers could control Berlin.