Extinction has been occurring naturally for millions of years and it continues to do so today. The current problem is that species are becoming extinct because of humans. One reason is that there are more people on the earth every day. More people require more space to live in and more natural resources, such as land to farm or build on. Other organisms have to compete with people for space and natural resources.
People usually win.
Another way humans are endangering animals is by changing the environment. Each species has special adaptations suited to its habitat. If this habitat is quickly changed, the organism may not be able to adapt and so it dies. Look around your neighborhood. The buildings for house and stores and the parking lots and streets cover land that was once the home of plants and animals.