Certain chiefs in Eastern Nigeria were called warrant chiefs because they

During the colonial era in Nigeria, the British introduced the warrant chieftaincy system as a means of indirect rule. The system involved the appointment of some chiefs by the British colonial administration to act as intermediaries between them and the local population. These chiefs were given warrants or certificates which conferred on them the authority to rule over their people. They were chosen based on their loyalty to the British colonial authorities rather than their traditional positions or legitimacy. Therefore, the correct option is: "were created by the British".