[2] After Erchanger was executed on 21 January 917,[3] Burchard seized all his lands and was recognised universally as duke.
In 919, King Rudolph II of Upper Burgundy seized the county of Zürich and invaded the region of Konstanz, then the centre and practical capital of the Swabian duchy.
At Winterthur, however, Rudolph was defeated by Burchard, who thus consolidated the duchy and forced on the king his own territorial claims.
In that same year, he recognised the newly elected king of Germany, Henry the Fowler, duke of Saxony.
Henry in turn gave Burchard rights of taxation and investiture of bishops and abbots in his duchy.