Here's why:
* Alien Invasion: The show features a race of reptilian aliens called the Visitors who arrive on Earth with the pretense of peace and goodwill, but secretly plan to conquer the planet.
* Genetically Engineered Soldiers: The Visitors create human-looking "tanks" who are genetically engineered to be strong, obedient, and loyal to them. These "tanks" are used as soldiers and enforcers.
Note: There was also a reboot of "V" that aired from 2009 to 2011. While it shared the basic premise of alien invasion, it had some key differences in its portrayal of the "tanks" and the overall storyline.
If you're looking for a specific detail about the show, feel free to ask, and I'll do my best to answer!