There were two reasons for choosing the 15 August. Firstly, it was already a bank holiday The Assumption of Mary is celebrated on 15 August. Secondly, the ruling Prince at the time, Prince Franz Josef II, was born on 16 August. Therefore, Liechtensteins national holiday was created by combining the Feast of the Assumption and the Princes birthday.
After the death of Prince Franz Josef II in 1989 it was decided to keep the national holiday on the same day. In 1990 a law was passed establishing the 15 August as the official national holiday of the Principality of Liechtenstein.