The International Court of Justice (ICJ) is the principal judicial organ of the United Nations, established to resolve legal disputes between nations. Its jurisdiction is specifically limited to cases submitted by States, meaning sovereign countries, in accordance with international law. The ICJ's role is to settle these disputes and provide advisory opinions on legal questions referred by authorized UN organs. Therefore, Option A, 'Countries,' is the correct answer, as the ICJ exclusively handles inter-state conflicts.
Options B, 'Individuals,' and C, 'Both A & B,' are incorrect because the ICJ does not have jurisdiction over individuals. Cases involving individuals, such as those related to war crimes or human rights violations, are typically addressed by other international bodies like the International Criminal Court (ICC) or national judicial systems, not the ICJ. Option D is incorrect as Option A accurately describes the ICJ's mandate.