Demolitions is the engineering discipline of demolishing and clearing structures that are no longer needed. Certainly, military combat engineers conduct demolitions against enemy buildings, but they have a wide range of other duties, just as civilian demolition is a skilled but routine construction and engineering discipline needed to make way for new construction.
Methods of demolition include structural weakening of buildings, by manually, with cutting torches on metal beams or explosively removing strength members, so they collapse of their own weight.
Explosives are widely used to force the building collapse, most dramatically in controlled implosion, a feature on television news, where a relatively small amount of explosions cause the building to fold gracefully, like a house of cards. The wrecking ball, a heavy metal hammer on the end of a crane boom, is a controllable yet brute-force means of demolition.
Proper demolition needs much engineering planning, so the demolished structure falls inside a safe area and does not damage other objects. The demolition process must be made safe with respect to buried and underground pipelines, power lines, and other infrastructure.