Final answer:
Countries needed to promise to respect international laws before joining the League of Nations, which involved committing to collective security principles designed to maintain global peace and prevent future wars.
Step-by-step explanation:
Before joining the League of Nations, countries needed to promise to give effective guarantees of their sincere intention to observe their international obligations. This commitment indicates that they must respect and adhere to international laws and engage in collective security. Therefore, the correct answer to the question is A) To respect international laws.
The covenant of the League of Nations established principles upon which member states were expected to operate, including the defense of each other against military threats, as outlined in Article X. This agreement was intended to create a balance of power by ensuring equal standing among member nations in terms of their military capabilities and commitment to peace.
The United States Senate, concerned about the implications of joining the League, notably the potential loss of their constitutional power to declare war and the fear of being drawn into international disputes, led to the US choosing not to join the League. This decision significantly weakened the League's ability to enforce its principles of collective security and mediate international disputes.