I remember reading this novel when I was younger and here are some of the details I remember:
Earth has a space station that is used as a main defense against aliens, however, I believe the Earth also had a space fleet. The aliens would only attack the top 20 'tribes' on the planet since Earth hadn't unified yet. Earth also has an AI that shoots down missile barrages aimed at the planet that performs better than expected. Earth also has a satellite that shoots a powerful laser that destroys alien space ships.
Also, humans use the wrecks of alien space ships to make missiles. There is also one scene where someone has to fly a fighter into a hanger at full speed and it gets posted on YouTube.