Zombie War : games for defense zombie in a shelter

Sir! The zombie is coming! This is the last survival base for us!
Zombie is coming, and mankind is facing a desperate situation to become a walking dead. As the last commander of mankind, you must build a shelter to defend your people!
First you must upgrade your base to make it stronger and able to defend humans from being invaded by zombies.
Than, you must recruit some soldiers, lead them to fight back, and destroy the invading zombies.
The invasion of zombies will become more frequent and powerful. You must upgrade the defense towers, better equip the soldiers, and finally bring them Counterattack, attack the zombies' lairs, and expand the human living space.
Can you finally purify the world?