Argentine Tango evolved in Argentina (unsurprisingly), and especially around Buenos Aires, and also neighbouring Uruguay. It became popular from the 1890s, although early styles were viewed as for the lower classes or "common people", so tango tended not to be an activity for aspiring socialites of the time. The 1890s saw a population explosion for Buenos Aires and Argentina, as immigration brought in european settlers to work in the port of Buenos Aires and beyond in the pampas, both in agriculture and related trades. Of interest, it was reported that the gender balance in the city at that time was something like 4 men to one woman, so social skills, like proficiency in dance, would clearly be a benefit to the male population.
The real explosion for the rest of the world occured in the early 1920s, when tango first hit Paris. It became popular with the upper stratas of society and the gentrified tango (exhibited in the salon style that we often see today) was re-exported back to Buenos Aires, allowing the form to be shared with the upper eschelons of society back home. Interestingly, although described as "Argentine Tango", this is primarily a means to distinguish it from its Ballroom cousin; outside of the cities, it is more common to encounter the folklore dances, including chacarera, chamamé, and zamba than tango.
The development in tango was mirrored by (or followed) the evolution of tango music itself. The earliest music was a fusion of African and European influences, typified by a rather earthy, fun style. The miloguero style of dance fits this well, with steps, crosses and basic turns, being very grounded. The more elegant 'salon' style evolved somewhat later, as I mentioned earlier, and this is further evidenced in the music which evolved more legato, lyrical forms, whilst maintaining the essential tango 2 x 4 feel.
Not to confuse the issue, the genre of Argentine Tango also encompasses the Tango Vals (Waltz) and Milonga forms. The Vals speaks for itself, not quite as flowing in form as the Vienese Waltz, but certainly demonstrating a richness in content. By contrast, the milonga captures 'fun', drawing on the habanera rhythm (dum-de dum dum), and drawing on its African root. As a final point of confusion, "milonga" is also used to name a tango social dance event, as well as the dance form itself!
Now we often associate Argentine Tango with the show dance or choreographed presentations seen in shows and on TV. But these are an abstract form. The form typically practised at a milonga is inherently improvised, where the leader indicates the move as an invitation to the follower, and the beauty is in the connection achieved by the couple and the way that they, in turn, interact with the ronda (the circuit of all the other dancers). The expansive steps and high kicks, flicks and aerial nonsense from the show dance has to be tempered for the space and conditions in the milonga, for the comfort and safety of everyone involved!
The dancers' posture and embrace is markedly different from that of the ballroom dancers. The main connection points are the clasped hand, opposing upper arm and hand, and especially the chest. So the posture can be more like an 'A' as the dancers come together. Like other dance forms though, the dancers use the floor, projecting hips downwards whilst extending the chest upwards, creating space for flexing, turning (and disassociating the movement of the upper torso from the hip). Both dancers typically maintain their own axis of balance (not leaning on each other for support), but there are exceptional movements - particularly the volcadas and colgadas - where the couple maintain a shared axis.
The music of Tango
Because Argentina was a largely closed country with political challenges, through the 1930 through to the 1950s (and even beyond), the music was able to develop without being tainted by the European or American popular music forms (of the United States). Around the 1950s, we really see a greater influx of influences - Piazzolla being a great example, combining as he does, the music of the milonga with classical and jazz influences, and more recently the nuevo tango and electro styles have evolved for a new generation. Nevertheless, traditional tango, and especially that of the "Golden Age" remain popular for social dancing and festivals around the world.
The music we hear today is that of the recorded orchestras of the day. In the 1930s, the record companies controlled availability of the music although many more would have been playing the milongas. As a result, there are well known orquestas (orchestras), conductors/directors and singers - known today through their recorded legacy. Amongst the good examples for listening are the orquestas of Carlos di Sarli, Juan D'Arienzo, Francisco Canaro and Miguel Calo. As you enter the world of tango, you will discover and enjoy many more besides.
What was the orquesta? The Orquesta Tipica (typical form) had no percussion or drums, unlike the folklore dances popular across Argentina. The instrumental ensemble typically had piano, double bass, 3 to 5 violins and 3-5 bandoneons. A singer frequently augments this and occasionally a cello may swell the ranks, or a flute or (muted) trumpet. The rhythm or percussive element is provided by the instruments in the ensemble; articulating and accenting notes, and also delploying effects such as tapping or banging the instrument's body. Articulation and accents would be a topic in itself, added to the instrumental effects contributed by, for example, violins playing the cotton windings (wrong side of the bridge) next to the instrument's tailpiece. I can just add that all string players use a lot of rosin on the bow, to achieve very clear and strong accents.
Of course, nowadays tango music is often performed live by a guitar (also well utilised in the traditional folklore dance music) or solo bandoneon. This may be a reflection of the cost of bringing a full ensemble together, as well as the difficulty of finding even one bandoneon player, let alone a section of three to four. Some would say that the bandoneon (a form of button accordion originating from Germany) is the instrument most famous for contributing a soulful, pained, expression to the tango music we know. It was originally used in small chapels that could not afford a pipe organ, across Germany.