Why is Japan called Japan?

The English word for Japan came to the West via early trade routes. The early Mandarin or possibly Wu Chinese (吳語) word for Japan was recorded by Marco Polo as Cipangu.
In modern Shanghainese, a Wu dialect, the pronunciation of characters 日本 'Japan' is Zeppen [zəʔpən]. The old Malay word for Japan, Jepang, was borrowed from a Chinese language - Jih'pen'kuo, and this Malay word was encountered by Portuguese traders in Malacca in the 16th century. Portuguese traders were the first to bring the word to Europe.
Japan is called that because someone misunderstood the Japanese word for Japan and used that as the English word for Japan.