Earth

Earth is the main setting of the MCU, and was the planet upon which lived the Human Race. It was the third planet from its Sun and was known to the people of the Nine Realms as "Midguard". After Thor Odinson of Asgard was exiled there, he made it his duty to protect it, as it was the home of his lover Jane Foster. (FILM: Thor).

SHEILD Director Nick Fury formed The Avengers Initiative to "make a statement" to the Nine Realms that Earth was ready for war. (FILM: The Avengers)