Released in the 70s, what was "Space Invaders"?

The “Space Invaders” arcade video game is an iconic piece of software, credited as one of the earliest digital shooting games. The message in “Space Invaders” is as basic as the graphics: When faced with conflict, players have no option except to blast it away. Avoiding an enemy only delays the inevitable; players cannot move forward or back, but can only defend their space. There’s not even a reason why the invasion is occurring. Players know only that the invaders must be destroyed. It’s a distinct cultural perspective, emphasizing shooting over everything else.

Source: Smitshonian Magazine