Self-defense systems are martial arts that are used to protect oneself from physical harm. Judo and Karate are two popular self-defense systems that have been practiced for centuries. Judo is a Japanese martial art that focuses on throws, joint locks, and pins. Karate is a Japanese martial art that focuses on striking techniques such as punches, kicks, and blocks. Both Judo and Karate are effective self-defense systems that can be used to protect oneself from physical harm.