" Fëanor realized that he had no way of transporting his army. Middle-Earth and Aman were at this point connected by Helcaraxë - a region which was immensely treacherous and bitterly cold even for the resilient Elves at the height of their power, and the shifting ice was deemed to be impassable for a force this size. "

Watch the full Middle-earth First Age animated video here:
https://www.youtube.com/watch?v=ojpCQ7_nweg&list=PL2Qq-rUSt7b1P4htSWJv3UUPP5E0HcquL&index=21