This is an alternate timeline to the one in which the Avengers live in, existing with altered events.
This timeline emerged as a new reality when Doctor Doom altered a few events in the original timeline, creating a whole new timeline with different situations and outcomes. When this reality came into existence, the original became non-existent because of the alterations in its history.
Doom went back in time first to Tony Stark before he even became Iron Man, back when he was attacked in Afghanistan. He offered Stark a place in his Empire and so Tony was saved and he never became Iron Man.
With these enhanced individuals and an army of Doombots, Doom conquered the Earth and its people, making his dream of conquest come true. However, a few heroes Clint Barton, Sam Wilson and Peter Parker refused to submit and formed a renegade team The Defenders.