What is the major cause of the disappearance of species?

Answer 1

Game hunters usually kill them off. like Hunters and stuff but theres other contributing factors now such as air pollution and global warming

Including the entire history of Earth, the majority of the world's extinctions have had nothing to do with human intervention. There isn't usually one major cause of a specie's disappearance, but a chain of interrelated events to which they cannot adapt. If you had to pick one cause - it would probably be changes in the habitat or environment which could include things like shrinking territory, limited gene pool, climate, available food, and competing organisms.