Some major factor responsible as threat to nature are as follows:
1) increasing human population: the exponential growth of human population has led to deforestation, ecological imbalance and reduction of wildlife.
2) exploitation of plants and animals: plants are useful for medicinal purposes and some plants have the potential to cure cancer which has led to huge exploitation of them, as well as animals like tigers are hunted for their bones.
3) poor and sluggish efforts of the govt.: due to corruption and various other things the govt. is usually unable to apply a firm and strict rule or law to conserve animals.
3) industrialisation: modern advancements and set ups of mega industries has mainly led to water pollution and air pollution since, factories release harmful gasses and waste materials in water and air.
4) nuclear powerplants: nuclear leakage can cause huge damage to a nation and its land due to high radiation and toxicity of the material.
5) plastics: plastics have been very important and useful in almost everything but they are harmful since, it doesn't get decomposed at all even for centuries!