Simplify the following text for a Grade 10 native English-speaking person.
Original: Next the Babylonian armies conquered the remaining northern states , including Babylon 's former ally Mari , although it is possible that the ` conquest ' of Mari was a surrender without any actual conflict .
Simplified: He then attacked and conquered the remaining cities in northern Mesopotamia , including Babylon 's former ally Mari . It is possible that Mari surrendered to Babylon without any fighting happening .