Exonym and endonym
Another reason why a country might call another country a different name is because people from a certain country might have different ideas about those people or associate them with certain things. For example, even though Greeks call their country Hellas, their country is known around the world as Greece because the Roman Empire named the region after Magna Graecia, which were coastal areas in southern Italy that were colonized by Greeks in the early days of Rome. Germany has a very large number of exonyms, being called Allemagne in French, Niemcy in Polish, and Saksa in Finnish. This is because Germany has interacted with many other European countries and the Germans were a collection of tribes speaking similar languages until they unified into a country in the late 19th century. Even though the Dutch call themselves Nederlanders in their own language, English speakers call them Dutch (a cognate of the German word Deutsch) because the words German and Dutch used to be interchangeable until Germany unified in the 1800s. From then on, German was used to describe people from Germany, while Dutch was used to describe people from the Netherlands.