Before 1415
In Frankish-Carolingian era the territories to the left of the Reuss belonged to Aargau, while those to the right were part of Thurgau. Starting in the mid 9th century this area became known as the Zürichgau. After the extinction of the Counts of Lenzburg in 1170, their land in the Aargau went to the Habsburgs. During the 10th century, they acquired vast tracts of land in the region. The Habsburgs granted the low justice rights over many of the villages to Hermetschwil and Muri Abbeys.
After the Swiss Confederation became independent from the Habsburgs, the new Confederation began to expand. After the expansion to the Acht Orte (Eight Cantons), they began looking for further territory. As the city of Lucerne grew in power, they became interested in the southern portion of what would become the Freie Ämter. In 1394 they acquired the Amt of Merenschwand which gave Lucerne an exclave west of the river Reuss. In the Battle of Sempach, the Habsburg villages of Aristau and Meienberg were destroyed. Following the defeat of 1386, and despite the 1394 peace between the Habsburgs and the Confederation, the Habsburg city of Bremgarten entered into an alliance with Bern in 1407.
Read more about this topic: Freie Ämter, History