Bacteria defeat the aliens in War of the Worlds. Create a fictional epilogue which reveals that bacteria have won many times before against many previous alien invasion attempts. They are the true defenders, perhaps even sinister or selfish in keeping Earth as a playground for only themselves and their toys.
Tell stories of other invasions: aliens versus dinosaurs.
Tell stories of the reputation Earth has among alien civilizations that have tried to invade and failed. Perhaps invading Earth is an absolute last resort, an act of desperation well understood likely to be an act of suicide.