Wikipedia notes that alien invasion movies aren’t really about lizards occupying the earth as much as an expression at some level, of our deepest social fears.
The invasion scenario has been used as an allegory for a protest against military hegemony and the societal ills of the time. Wells’ The War of the Worlds is often viewed as an indictment of European colonialism and its “gunboat diplomacy” —setting a common theme for some politically motivated future alien invasion stories.
Prospects of invasion tended to vary with the state of current affairs, and current perceptions of threat. Alien invasion was a common metaphor in US science fiction during the Cold War, illustrating the fears of foreign (i.e. Soviet Union) occupation and nuclear devastation of the American people. …
Some of the elements of the genre are the need for a temporary truce among all of us to fight the transcendent danger posed by “them”. But often the line between friend and foe is unclear. While in the War of the Worlds the Martians looked like the Martians in many other scenarios, the invader looks like one of “us”. If the allegory theory is at least partially correct, future generations might ask, in 2009, when the producers created the TV series, what fear was V playing on? Who are the “they”? And for that matter, who are the “we”?