Martial Arts have been around since there was a need for conflict resolution. The study of conflict and how to gain the best advantage from conflict are the basic building blocks of Martial Arts.

There are several schools of martial arts, each with it's own flavor and character. Some examples;

Karate
This martial art was originally designed for unarmed peasants to take on fully armoured soldiers. Strikes are linear and extremely strong, as practicioners were not expected to get a second hit.

Judo
Literally translated as the soft way, Judo is best known for it's throws and joint locks. Originally based on Ju Jitsu, Judo is now an Olympic Sport.

Aikido
Inspired by Samurai in Japan as the combat art of last resort after being disarmed. This art promotes harmony between you and your opponent, and almost all moves are reactions to attack.

Boxing
In it's many forms, boxing is probably the most universal martial art. Many cultures consider fighting on the ground to be uncivilised, so boxing emphasizes punching.

Capoera
Masked as a dance, Capoera was a martial art taught between slaves in Brazil. Because the hands were almost always shackled, Capoera uses wide sweeping kicks and handstands.

Ninjitsu
A martial art mostly praticed by Americans.


There are many other forms of martial arts.

An art form primarily associated with combat. Like dance, combat can be formalized from an instinctive act of belligerants into a set of rituals, techniques, and forms.

It is worth noting that the Japanese consider all art forms associated with the samurai class (collectively bushido) to be martial arts, despite many of them, e.g. go-do, or the tea ceremony, having a dubious connection to combat at best.

A fairly comprehensive list of specific martial arts can be found in that node.

There's a few wrong facts that should be cleaned up. Hopefully I don't get into a rant.

The first is Karate, which was an art style emphasising bare handed fighting, and was taught only to the rich. This old Okinawan art was once called "te", or 'hand', and 'kara', or way, was added through time. There is substantial proof that only the rich learned the martial art.

-Okinawa was mainly a farming country, like many cultures back in the day, and no citizen would have the time or energy in order to practice martial arts after their chores.
-The Japanese, who took over the island, did not exactly "take over". Both Japan and China claimed they had rights to the island for a long time, until Japan finally stepped in and overtook the island in 1609. The Okinawians fought for three days before they threw in the towel and let Japan in. They weren't terrorized by the uber-evil Samurai, either.
-The Okinawan's leader were to blame for banning civilians to hold weapons, and it was a long time before Japan showed up that this happened.
-Fighting Samurai, warriors trained since childhood to kill, with pitchforks and bare handed techniques is one of the biggest karate farces of all time. They never fought back; if they did, they would be captured by a league of Samurai, tortured, and crucified (it was one of their favorite too).

The next thing I want to clear up is Ninjitsu. This was an overlaying art used by ninja hundreds of years ago. It stressed survival in the enviorment and stealth over fighting. Most ninja were used liked the spies of today, seeking to blend in for reconnaissance. It was also a weapon art, and had many sub martial arts within it (the names which I cannot remember), which had positions such as "weapons," "natural herbs and poisons," and "hand to hand moves." I'm sad to say, but most ninjitsu learned today is a bullshit hybrid of its former self. This is because the most successful ninja were the ones we never heard about, and the most successful ninjitsu only taught by selection.