Complex sentence: Sigismund became a strong king that conducted a lot of improvements in the Hungarian law system and rebuilt the palaces of Buda and Visegrád, bringing materials from Austria and Bohemia, ordering the creating of the most luxurious building in all central Europe.
Split into simpler sentences: Sigismund became a strong king who created many improvements in the Hungarian law system and who rebuilt the palaces of Buda and Visegrád. He brought materials from Austria and Bohemia and ordered the creation of the most luxurious building in all central Europe.