Please reject the advice from the commenters suggesting to feed your cat a vegan diet. Cats are obligate carnivores and must have meat in their diet to survive-there have been instances where a cat or kitten was fed aa vegan diet and became so ill they almost died. Here is a short article about why cats can’t survive on a vegan diet: https://www.aspca.org/news/why-cant-my-cat-be-vegan
Do you mean just the human population would go vegan? Or do you mean eliminating all carnivores? That wouldn’t be possible, as carnivores keep the eco systemin balance by removing sick and weak animals.