47MartialMan:
Capoeira isn't really about combat. Some techniques from Capoeira can be assimilated to create an effective martial art, but not Capoeira in itself. Can you win a bar-fight with it? Probably not; most moves take time and space, though some techniques are very effective and resemble San Shou take-downs.
Capoeira is a game. Though it does incorporate combat, it's more akin to a game or dance. Think Dance Dance Revolution. It's a game about dancing, but everyone knows that nobody dances that way; the same with Capoeira, it's a martial art that is performed through dance, but no one fights that way.
Capoeira is about rhythm. The main stance is called the "ginga". It's a triangular patterned movement that keeps the fighter mobile. A technique is executed from the ginga, and it is exited from it as well, creating the "flow" or the "dance" as you would call it.
Capoeira is "played" in a game called a "roda". The object of this game is not to best your opponent by pummeling them to dust, but to display your technique with precision and flow, keeping the game moving.
Even though Capoeira isn't necessarily suited for combat, there are some nasty and brutal techniques in Capoeira that don't exist in any other martial art. However, these techniques never connect because of the very nature of Capoeira in which the object of the game is to keep the dance going. The Escorpianado, in which you roll up onto a handstand, and snap back forward with your legs, is designed to crush your opponent's leg or back as they're sweeping. Of course, this technique is never performed in a roda because it would effectively end the dance. Other effective techniques include the the S-dobrado, armada, parafuso, and mariposa.
On the historical background of the martial art, as someone mentioned before, yes, Capoeira began as a martial art disguised through dance by African slaves. A lot of people associate Capoeira with Brazil however. This is because there are two types of Capoeira. Capoeira Regionale and Capoeira Angola. Capoeira Regionale is the Brazilian form while Capoeira Angola is the original African form. The reason it developed in Brazil is because African slaves were part of the regular slave trade there. Simple as that.
Capoeira Angola tends to be more rustic in nature, based more on dance, music and flow than on flashy movements. Capoeira Regionale on the other hand is all about flair. Spinning kicks, cartwheels, handstands and flips.
Cool clip from a movie demonstrating a scripted fight between a Capoeirista and a Muay Thai fighter.
http://youtube.com/watch?v=moReN9l2ap0