Skynet vs. The Matrix
In the very far future, the world is taken over by machines. Half of the world is run by Skynet, half is under the Matrix. An uneasy truce lies between them, their respective machines don't cross over the boundary to the other side.
Skynet however learns that the Matrix houses a human farm called Zion and Skynet perceives such a huge gathering of humans as a threat to itself. So Skynet decides to break the truce, invade the domain controlled by the Matrix, and attacks Zion with every robotic force he has (that we've seen through all 4 terminator movies).
The Matrix retaliates by sending all of it's sentinels against Skynet.
Which computer tyrant annihilates the other's forces? Who wins in the war of machines?
And just to make it more interesting, I wonder what would happen if aliens decided to invade Earth at this exact moment? Let's say the aliens from War of the Worlds. Would the Skynet and Matrix be able to stop an invasion?