Until the mid 17th century (Late Ming, Early Qing Dynasty), the only teas consumed in China were green (unoxidized) and oolong (semi-oxidized) teas.
The tale goes that while a passing army entered the Fujian province, they decided to take shelter at a nearby tea factory. This held up production at the tea factory, where leaves were left out in the sun, causing them to oxidize for a longer period of time and resulting in darker leaves. In an effort to accelerate the drying time, they decided to smoke the leaves over pine wood, thus creating Lapsang Souchong, which became one of the very first black teas.
Although compressed, post-fermented teas (pu-erh) were already known as “black teas” in China, the term was usurped by Dutch and British traders who began identifying Chinese “red teas” as “black teas” because of the color of the dark, dry leaves. Even to this day, Chinese “red tea” is still referred to as “black tea” in the Western world.