What are three reasons a species may become extinct?

Three reason for a species to become extinct are:

Climate Change: Each kind has their own defense systems and built in mechanism to fight epidemics and diseases, with the changing climate for some species it becomes hard to fight with the new epidemics and diseases causing their eventual extinction.

Spread of Invasive Species: When in an area a species is utilizing the resources and another invading species also start making use o that source the battle will end on the rule or "survival of the fittest" and one from the two will become extinct.

A catastrophic event / Natural disaster: At times there can be a single catastrophic event like a volcanic eruption or a meteor striking the earth etc. can cause an entire species to go extinct.