Strategic Thinking Exercise: Alien Invasion

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A hypothetical scenario:

Alien spacecraft have landed in North Africa. CNN, Peter Jennings, Dan Rather, etc... are reporting at the scene. George Bush, other world leaders and the UN quickly form delegations to greet the otherworldly visitors. The world is abuzz with the significance of the event. For a lengthy moment in time, no one could care less if Robert Blake did it, people's minds are off Osama Bin Laden's whereabouts, the Israelis and the Palestinians put their decades-long bloodbath on hold, and people's interest in the gyrations of the stock market goes on the backburner. Everyone wants to learn more about the alien visitors and their apparently advanced civilization/technology.

One week passes and it is realized that the aliens are:

1. Belligerent and warlike.
2. Likely bent on an invasion of the Earth.
3. Likely interested in enslaving or obliterating the human race.
4. Highly advanced militarily and technologically.

The alien craft leave soon after. It is very obvious that this is not the last engagement with them, but only the beginning.

What do you think would happen next strategically and politically? What should happen?