Complex sentence: After a short military career he was later accused of grand treason by the Austrian authorities and imprisoned, first at Ratteburg in Tirol and then at Schlossberg in Graz, where he spent the last 20 years of his life.
Split into simpler sentences: After a short military career he was later charged with high treason by the Austrian authorities. He was imprisoned first at Rattenberg in Tyrol and then at Grazer Schloßberg, where he spent the last 20 years of his life.