Complex sentence: In the resulting battle, Nirnaeth Arnoediad (Unnumbered Tears), they lost almost all their armies, and Morgoth conquered the entire North; and then he destroyed the remaining Elf-kingdoms one by one.
Split into simpler sentences: In the resulting battle, Nirnaeth Arnoediad (Unnumbered Tears), they lost almost all their armies and Morgoth conquered the entire North. Afterwards, he destroyed the remaining Elf-kingdoms one by one.