Hawk Castle of the Habsburgs
The Aargau is a region in the centre of the Swiss midlands and was Habsburg territory until 1415. The Habichtsburg (Hawk Castle) in the present-day village Habsburg was the castle that gave the dynasty its name. The Habsburgs, one of the many competing aristocratic families in this part of Europe ( Alsace, Switzerland, Germany and Austria) had acquired the territory after 1173. The fragmentation of the duchy of Swabia ended the previous political unity containing much of the Alps, including the territory of the former Roman province Rhetia, but nobody could have predicted their rise to power as German kings and Holy Roman Emperors, without interruption from 1438 until 1740, and as Austrian emperors until 1918. The Habsburgs controlled the Aargau by their Bailiff with seat in Baden.
This changed in 1415, when Swiss troops from various cantons seized the territory and conquered, but not destroyed the Habichtsburg. Possession of the rich territory was of great importance and the Aargau became not a (confederate) member, but a so-called Gemeine Herrschaft of the victorious cantons. It was politically relevant because the acquisition of Aargau closed the territorial gap between mighty Berne (and other cantons in the west) and the eastern confederates. Although they had lost the Aargau and one their (many) castles, acquisitions in Tirol and South-Germany more than compensated the loss for the Habsburgs and the rather loosely organized Confederation of sovereign cantons without federal institutions, let alone a united military force, offered good opportunities for Habsburg to regain the Aargau. The territorial and economic interests of the cantons differed and they were fully autonomous to conclude pacts with other powers. This happened between 1436 and 1450, when Zurich and Schwyz, supported by Berne, disputed territories in central Switzerland (the Toggenburg legacy). The Habsburg ruler Frederick III (1415-1493) took his chance and made a deal with Zurich. Frederick proposed Zurich a large part of the Torrenburg territories, in exchange Zurich would support Habsburg restitution in the Aargau and a new Confederation of eastern cantons, including and supervised by the Habsburgs.
The subsequent war, called the Old Zurich War (Alter Zürichkrieg), became truly European, when the (seven) electoral princes (Kurfürsten) of the Holy Roman Empire supported Schwyz, Berne and other cantons against Zurich and Habsburg, supported by the King of France. Zurich (and Habsburg) lost however and the Confederation became a key territorial power in the region, because no monarchic or urban military force was capable of defeating the Swiss troops and the self-confident, but loose Confederation dealt with Italian, Swabian, Habsburg and other princes as territorial peers and Swiss soldiers had established their (invincible) reputation (for the time being), which resulted in the lucrative mercenary business. The Habsburgs never returned to the Habichtsburg, but took control over large parts of central Europe instead. (Source: C. H. Church, R.C. Head, A Concise History of Switzerland, Cambridge 2017).