Simplify the following text for a Grade 7 native English-speaking person.
Original: `` Operation Number One '' ) was a campaign of a series of major battles between the Imperial Japanese Army forces and the National Revolutionary Army of the Republic of China , fought from April to December 1944 .
Simplified: Operation Ichi-Go ( or `` Operation Number One '' ) was a series of battles between the armies of Japan and China . The battles happened between April and December 1944 .