The tango is a sensual genre of music and dance that originated in Argentina. It is usually played by a tango orchestra consisting of strings, bandoneon, bass and sometimes piano, though various other Latin-based instruments are found outside of this core group. Each of these instruments can be represented in any number within the band; the specific instrumentation is part of the tango orchestra's uniqueness.
Most tango orchestras are full of extremely portable instruments, instruments that can be quickly packed up and easily traveled with. This bent towards portability is a strong reflection on the tango's underground origin. The tango originally started in the early 1900s as a sort of low-brow music in Buenos Aires. It was favored by gangsters and often heard in brothels, which accounts for the form's sensuality. The tango alluded a sense of decadence, a hedonism that the upper class found uncomfortable and bothersome, and they often did all they could to keep it out of their neighborhoods. Those playing the tango were usually tied in some way those listening to the tango, so they were constantly on the move. Portable instrumentation, for these early tango orchestras, was absolutely essential.
However, the constant playing of tango music in the Argentine streets eventually bore holes into the mainstream, and the upper class (despite their initial misgivings) eventually gave in to the sensuous, intimate form; it was altered and toned down into various commercial forms. By World War II, the tango was a craze in Argentina and elsewhere, bringing with it the dance of the same name.
The tango dance, unlike some forms of the music, managed to stay true to its peasant roots. The Argentine tango, a form sometimes found in modern times, is the original peasant tango, danced as early as just after the music's inception. A variation on the original tango dance eventually found its way to the United States, sweeping the country with its sensuous, sometimes complicated steps. A simplified version of this form eventually became the ballroom tango dance that is still danced today.