There are, generally speaking, two kinds of disasters that can occur in the world. These are natural disasters and man-made disasters.
Natural disasters are those which occur naturally. These disasters were not caused by human agency. A hurricane, for example, is a natural disaster. So is an earthquake. It is true that these events only become disasters because human beings have built cities where those events occurred. However, the actual event is not something caused by human beings.
By contrast, man-made disasters are disasters that have nothing to do with nature. These are things that happen when things that human beings have done go wrong. For example, one of the worst man-made disasters in history was the gas leak at the Union Carbide pesticide plant in Bhopal, India. Thousands of people were killed by this leak. This disaster was not caused by anything natural, but rather by a fault in a mechanism made by human beings.
Man-made disasters, then, are ones where the disaster happens only because of things that human beings have done.