There are different forms of drag including friction drag, form drag, and induced drag. Friction drag occurs in the boundary layer of air while form drag results when the airflow past an object breaks away from that object. This effect produces a swirling air that takes energy from the object. Induced drag deals strictly with aircrafts in that it is a drag due to the lift of that aircraft. It is the difference in pressure found above the wing and the pressure found below.
Induced drag causes a vortex, which holds the plane back.
In order to see how the knowledge of this field has progressed, one must start from the point where the interest in aerodynamics first was documented. In the 1400s, Leonardo da Vinci was the first reported person to have studied the flight of birds scientifically. In observing birds, he came up with fantasies of flying machines and drew sketches of them. He was the first person attributed with observing that air resisted the movement of solid objects. Up until that point in time, people had no real knowledge of the physical properties of air.