Complex sentence: On the journey to Aman, some of the Eldar (those who set out) became sidetracked; these notably included the Sindar, who stayed on the coasts of Middle-earth when their king, Thingol, became lost in the forest.
Split into simpler sentences: On the journey to Aman, some of the Eldar (those who set out) became sidetracked. These notably included the Sindar, who stayed on the coasts of Middle-earth when their king, Thingol, became lost in the forest.