Mars had an atmosphere, oceans,land masses, just like Earth.
BUT, they tainted their fresh water sources. They used up the fertility of their soil. All the land based life and plants died. The soil, no longer held in place by plants, turned into dust storms. Eventually the atmoshphere, for the most part vanished.
The atmosphere there, and here on Earth, is a system that is in a very delicate balance. The outer parts protect us from certain rays of the sun, and help to hold in the nitrogen/oxygen and other gases we breathe. These gases are put there BY THE PLANTS. If you destroy the ability of the soil to grow plants, it is not long before all landbased life dies. Without plants to regenerate the atmosphere, the balance of the layers in the atmosphere is corrupted, and it slowly dissipates. The land is ravaged by wind storms, all signs of life are covered over with dust, and eventually the oceans freeze.
This is what happened to Mars, and we will make Earth the same, if we are not more careful.