1st wave: An electromagnetic pulse wipes out all technology, including cars, airplanes, cell phones, etc.
2nd Wave: The Others (the aliens) drop a huge metal pole on one of the fault lines, causing a massive tsunami that wiped out all of the costl cities on all seven continents.
Wait! I'm a human!
Sure you are!
3rd Wave: A very contagious disease (which is referred to as the Red Death, the Plague, Blood Plague, etc.). It is carried around the world by birds, wiping out 97% of the surviving population.
4th Wave: The Others don't look like anything. They take control of the consciousness of living creatures. That is what they do in this wave. They take control of humans, but the actual humans don't know if other people are human or alien, causing them to not trust anybody.
5th Wave: Getting the humans that they have infested to wipe out the human race by sending brainwashed children, highly trained in combat, to wipe out what they think are the Others. World Domination.
Brainwashed kid thinking that he is killing an alien.