The Habsburgs

The Habsburgs were one of the most important royal families in Europe. At the time of the play, the Habsburg empire was also much bigger than Austria is today. "With a population of 56 million, the empire had developed over the course of the centuries into a multi-ethnic monarchy in which many different nationalities, including Germans, Hungarians, Czechs, Rumanians, Slovakians and Italians, lived under the one crown." (see http://www.schoenbrunn.at/en/things-to-know/the-habsburgs/franz-joseph-i.html

The Habsburgs formed major alliances between countries often through marriage. Marie Antoinette was first a Habsburg princess before becoming an (ill-fated) French queen. Napoleon's second wife was a Habsburg.

You can learn more about the dynasty and empire here:
http://www.habsburger.net/en/