Obviously this scenario is based on the movie World Invasion: Battle Los Angeles. There are 30 Human Civilizations and 1 Alien. You can play as any one of the human factions or as the aliens.
All human factions are in a locked alliance against the invaders. The nations that are on the frontlines against the aliens will be the hardest to play as early on as they will have to bear the brunt of the invasion without being fully mobilized. During playtesting I found that the USA and China seem to hold their own pretty well, while the Mexicans, South Americans, British, and Pacific Islands get crushed. The Aussies take a pretty good beating too.
From what I observed during testing, the frontline nations should really just try and hold the line (easier said than done) until all the other factions mobilize to bring enough force to drive the aliens back. Basically, you have to defeat the aliens with overwhelming numbers because your units are significantly weaker than the aliens'.
Playing as the aliens, SPEED IS KEY. Make use of your Insertion Pods to out manuever the humans and disrupt their attempts to mobilize. Your units are stronger, but they won't completely dominate the battlefield. If you are not quick enough, or you get bogged down on the frontlines, the humans will overwhelm you with their numbers. Your forces are also scattered across the globe, so you will be fighting on multiple fronts. Do your best to consolidate your positions and, again, use your Insertion Pods to allow your forces in different parts of the world support each other.
One final note for the aliens: Do not let the humans retake or destroy Los Angeles. If you allow this to happen you will lose the Alien Command & Control wonder, which puts an Alien Drone Control in every city. This Drone Control auto-produces the Wedge Ship (the aircraft from the film) every five turns. So if you lose Los Angeles you lose your valuable air support, which will most certainly spell defeat for you.
Due to time constraints caused by my job and the fact that I'm about to have a baby, I needed a good scenario to act as the base-template for this one. This is why I used MeteorPunch's amazing Modern Age 2: First Strike Scenario as the base for my scenario. I would like to give him the thanks he deserves, as he is just as responsible for this scenario existing as I am.
Also for the full list of unit and graphic makers that deserve credit, check out the thread for MeteorPunch's scenario thread.
And now the link for the actual scenario: Updated World Invasion
Have fun and enjoy!