Complex sentence: Many right-wing politicians complain about threat of a "nation-death", that is the Magyars will soon disappear from the face of Earth, as most couples have only one children or none at all.
Split into simpler sentences: Many right-wing politicians complain about threat of a "nation-death". They worry that the Magyars will soon disappear from the face of Earth, as most couples have only one children or none at all.