Shiite militias are armed groups primarily composed of members from the Shia branch of Islam. They often form in response to perceived threats and conflicts, particularly in regions where Shia communities are a minority. These militias can vary in size and organization, with some being formally integrated into national armed forces, while others operate independently. In countries like Iraq and Syria, Shiite militias have played significant roles in combatting extremist groups such as ISIS. They are often supported by regional powers like Iran, which provides training and resources, influencing the political and military landscape in the Middle East.