Complex sentence: Steiner and a group of prominent German theosophists founded a new society, the Anthroposophical Society in December 1913; they were excluded from the Theosophical Society in January of 1914.
Split into simpler sentences: Steiner and a group of prominent German theosophists founded a new society, the Anthroposophical Society in December 1913. They were excluded from the Theosophical Society in January of 1914.