julus Caesar and octavian
Monarch
no
a monarchy (British)
A country with no hereditary ruler; the head of state is elected
The Monarch (generally a hereditary King or Queen).
Their ruler was an hereditary king.
The United Arab Emirates does not have a king, it has a hereditary ruler who is normally the president of the country. In 1991 the ruler was HH Sheikh Zayed (father of the current ruler)
monarchy
Of course there's a difference. A queen is a ruler while a princess is the daughter of a ruler. In today's high European society, sometimes a woman has the title "princess" as it may be a hereditary connotation or she may have married a man who's is a hereditary prince of something.
Monarchy is a generic term for a (usually) hereditary ruler such as a king, queen, emperor, caliph, sultan etc.
The Ottoman sultan was the autocratic hereditary ruler of the Ottoman Empire. (Basically it was no different than a king).
Not really possible to answer as Africa is a continent; in history is was not governed by modern geo-political boarders and was basically "tribal" - that is to say independent tribes each ruled by an elected or hereditary ruler.