Agents of STRIKE
Codename: Machine Earth
Earth-209 was the first alternate universe that ARMOR visited using the Holepunch. It is also the first alternate universe to strike back at us.
Earth-209 is inhabited by Synthezoids, machine-people who seem to have replaced humanity entirely. There is no organic life left on Earth-209, only machines. Synthezoids resemble humans in many ways, and are emotional artificial intelligences capable of fear, anger, hate, and, theoretically, love. They also seem to reproduce on their own, although the process is unclear to use.
We were unable to obtain the full history of Earth-209 on our first (and only) exploration of the world, because the Synthezoids are zealously hostile to all organic life. The Exploration Corps was immediately attacked and had to escape after first contact, and then the machines somehow reverse-engineered our technology in a matter of months and sent a vanguard to prepare for an invasion of our world.
That vanguard was defeated, fortunately, and this incursion incident led to the creation of the Ultimates.
There have been no further incursions from Machine Earth we are aware of, but the Synthezoids now possess multiversal travel technology and their attack could come at any time. We need to be ready.