A monarchy is a form of government, in which one legal person or a small group of persons has all power until death or abdication. The amount of power varies between no power to all power. Many monarchies are a democracy today. Their named a crowned monarchy or constitutional monarchy. The leader of a monarchy is called a monarch, but the exact title varies per country.
Most monarchies today are a kingdom. These are Spain, the United Kingdom, the Netherlands, Belgium, Denmark, Norway, Sweden, Morocco, Saudi-Arabia, Thailand, Bhutan, Jordan, Lesotho, Bahrain, Cambodia, Eswatini, Tonga and the French overseas area of Wallis and Futuna (has 3 kings). Japan is an empire and is ruled by a emperor. Luxembourg is a grand duchy and has a grand duce. Liechtenstein, Andorra and Monaco are principalities and have a prince (Andorra has two princes). Other monarchies are Malaysia, the United Arabic Emirates, Brunei, Oman, Qatar and Samoa. Vatican City is also seen as a monarchy.
After the Age of Enlightenment and the French Revolution most countries went from a absolute monarchy to a constitutional monarchy. The power of the monarchs was hand to the parliament and the people of the country. Most new countries decided to be a republic, with a chosen leader (president). France even abolished its monarchy. After the First World War many countries abolished the monarchy. Former monarchies are Germany, Portugal, Italy, Greece, Russia, Finland, Austria, Brazil, Mexico and China.