Complex sentence: The Regency of Hungary, officially called the "Kingdom of Hungary" was a de facto regency state that existed from 1920 to 1946 under Regent Miklos Horthy officially representing the abdicated Hungarian monarchy.
Split into simpler sentences: The Regency of Hungary, was a de facto regency that was officially called the "Kingdom of Hungary". It was the Hungarian state that existed from 1920 to 1946 under Regent Miklos Horthy officially representing the abdicated Hungarian monarchy.