The main resource that the settlers are protecting in "Mad Max 2: The Road Warrior" is gasoline. In the post-apocalyptic world of the film, gasoline is a precious commodity due to its scarcity, making it a central point of conflict as various groups struggle to control it for their survival and dominance. This focus on gasoline underscores the movie's themes of desperation and the lengths to which people will go in a world stripped of its resources.