All around the world countries have weapons that could kill millions. There are enough nuclear bombs around the world to kill almost all life on earth and governments fund projects to make new weapons to get them ahead of the other. During the cold war the U.S. and the Soviet Union didn't fire because of fear of retaliation. The retaliation would cause death to almost all of the opposing country.
The way the planet gets treated and eveything that everyone uses is disposable is going to either cause us to drown in our own filth, or the greed of corporations is going to poison the resources of the earth, and it will cause the end of humanity like that. Either way a change is needed
If we stay on the path that we are on as a species, we will most definitely be the cause of our own extinction. First of all, we are using precious and rare resources at an alarming rate. Secondly, artificial intelligence is theorized to get to a point where it could surpass human intelligence and cause all sorts of issues.
The human species will eventually self-destruct and be the reason we fall. Nobody does more harm t the human species than we do to ourselves. It is sad but true. We as a species destroying ourselves is almost inevitable in my opinion. It is going to happen sooner or later.
There are a great number of natural occurrence that could destroy us before our blatant disregard for nature would ruin us. For example all of the theories on how the dinosaurs became extinct would surely kill us as well. Whether it be from a meteor, ice, age, a plague, lack of food or a combination of them.