Simplify the following text for a Grade 5 native English-speaking person.
Original: The Å nin War was a civil war that lasted 10 years ( 1467 â `` 1477 ) during the Muromachi period in Japan .
Simplified: The Å nin War was a civil war in Japan . It lasted 10 years ( 1467 - 1477 ) during the Muromachi period .