Upper Saxony
It was particularly to distinguish the lands from 'Lower Saxony', a concept which arose later in popular usage (though never enforced) as a term for the original Saxon lands in north and west Germany (where Low German dialects had spread), in what is now the state of Lower Saxony, as well as the adjacent Westphalian region, Holstein and the western part of today's Saxony-Anhalt north of the Harz range (Eastphalia).
Duchy of Saxony
In 1152 Henry supported his cousin Frederick III of Swabia to be elected King of Germany (as Frederick I Barbarossa), probably being promised to regain the Duchy of Bavaria in exchange. Henry's dominion now covered more than two thirds of Germany from the Alps to the North Sea and the Baltic Sea, making him one of the mightiest ruler in central Europe, and thus also a potential threat for other German princes and even Barbarossa.