Hot air balloons are the oldest successful human-carrying flight technology, with two key parts - an envelope or bag and a gondola or basket. They require a source of heat, as heated air inside the envelope makes the balloon buoyant and able to rise to extreme altitudes. The Montgolfier brothers, Jacques-Etienne and Joseph-Michel, are credited with developing the first hot air balloon in the late 1700s in France. Their early demonstrations included launching a balloon filled with smoke and later carrying animals aloft. Balloons went on to be used for military observation during conflicts like the American Civil War.