Collective security is difficult to apply successfully for several reasons. It requires binding agreements for countries to take collective action against aggression, but defining aggression and getting unanimous agreement is challenging. It also depends on having enough collective power and political will to deter or quickly repel aggressors. However, getting universal participation is nearly impossible, as countries have their own strategic interests. This undermines the goal of a true community of power acting for the security of all. Historic attempts at collective security through the League of Nations and UN have struggled with issues of defining the community to protect, determining the agents of enforcement, establishing the required capabilities, and balancing state sovereignty with collective authority. Lack of US participation and exemptions for strategic interests weakened the League