Thailand's charters and constitutions have recognized a unified kingdom with a constitutional monarchy, but with widely differing balances of power between the branches of government. Most Thai governments have stipulated parliamentary systems; however, several of them also called for dictatorships, e.g., the 1957 Constitution. Both unicameral and bicameral parliaments have been used, and members of parliament have been both elected and appointed. The direct powers of the monarch have also varied considerably.