Complex sentence: This could refer to the Master Chief's never ending battle and how he has returned to battle the Covenant again and again or it might be reffering to the fact that the Chief has been to more than one Halo.
Split into simpler sentences: This could refer to the Master Chiefs never ending battle and how he has returned to battle the Covenant again and again. It might also be reffering to the fact that the Chief has been to more than one Halo.