Complex sentence: Aged six, Tomasz entered the Academy of the Cadet Corps of His Majesty and of the Republic of Poland (the military cavalry school)-his first two years there were spent learning foreign languages, artillery science and fencing.
Split into simpler sentences: Aged six, Tomasz entered the Academy of the Royal Cadet Corps (the military cavalry school). His first two years there were spent learning foreign languages, artillery science and fencing.