The martial race theory is a way of thinking that suggests that some people are born better at fighting than others. People who believed in this theory thought that there were certain ethnic or national groups of people who were better warriors, or better fighters, than other groups. This idea was used in the past in some countries, for example India or Sri Lanka, to decide which people should be recruited into the army. They believed that the people from certain groups were better suited for this because they were born to be naturally better at fighting than other people.