Complex sentence: When the Fellowship was broken, he tracked the hobbits Meriadoc Brandybuck and Peregrin Took with the help of Legolas the elf and Gimli the dwarf to Fangorn Forest and fought in the battle at Helm's Deep and the Battle of the Pelennor Fields.
Split into simpler sentences: When the Fellowship was broken, he tracked the hobbits Meriadoc Brandybuck and Peregrin Took with the help of Legolas the elf and Gimli the dwarf to Fangorn Forest. Then he fought in the battle at Helm's Deep and the Battle of the Pelennor Fields.