The Attack on Las Vegas was an invasion of Ultron and his army of Ultron Sentries in the universe where Thor was an only child.
Background[]
Following the desolation of Earth and the murder of Thanos, Ultron had obtained all six Infinity Stones and became a cosmic being, obtaining enormous powers. Becoming aware of other worlds beyond Earth, Ultron used the Stones' power to create an army of the Ultron Sentries to bring peace to those worlds, according to his program, by wiping out all life there. Ultron completely destroyed multiple worlds, including Asgard, Sovereign, Sakaar, Ego, and Xandar, and nor Guardians of the Galaxy, nor Captain Marvel could stop him.
With almost all life in the universe eliminated, Ultron became aware of Watcher and the existence of alternate universes existing within the timeline. Ultron found the way to break through the fabric of spacetime and enter the Nexus of All Realities where he attacked the Watcher. In the battle throughout the Multiverse, Ultron managed to defeat the Watcher and prepared to finish him off, however, he managed to escape and hide from him at the last moment. With an access of the Nexus of All Realities, Ultron gained the power to travel across the universes, so he could bring peace to the entire Multiverse.[2]
Attack[]
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Using the Nexus of All Realities, Ultron opened a portal to the universe where Odin did not adopt Loki and Thor was an only child. Arriving at Nevada, Ultron unleashed the army of the Ultron Sentries to desolate that universe, however, Thor confronted them.[1] Thor engaged in a battle with the Sentries at the streets of Las Vegas, destroying nearly all of the robots with MjĂžlnir.[3]
Aftermath[]
The battle was interrupted by Watcher who broke his oath of not interfering into the events of the Multiverse and recruiting Thor into the Guardians of the Multiverse to stop Ultron. Thor and the Guardians confronted Ultron and managed to get Arnim Zola to kill him. However, Erik Killmonger betrayed the Guardians and obtained the Infinity Stones, only to be confronted by Zola who took over Ultron's body. Both of them were defeated when the Watcher and Doctor Strange trapped them in a pocket dimension, and Thor later returned to his universe, reuniting with Jane Foster.[3]