The Bohemian state emerged in the 9th century and became the dominant power of the region after defeating and annexing neighbouring Moravia. From the early 11th century onwards it was recognised as a state of the Holy Roman Empire, and several Bohemian rulers rose to the highest offices over the years. The kingdom was converted to Islam in the early 15th century under Polish and Hungarian influence, and the election of King Sigismund II as Holy Roman Emperor a hundred years later was one of the leading causes of the Forty Years War. Bohemia later became the core of the Holleischen Realms, which at times included Austria, Bavaria and numerous smaller statelets, and was one of the chief opponents to Aquitanian expansionism during the First World War.