The American Space Leadership for the 21st Century Act authorizes the Secretary of State to lead diplomatic efforts to protect and strengthen U.S. space security against growing threats from adversaries like China and Russia. The legislation empowers the State Department to assess space threats, work with allied nations to develop shared space capabilities and security standards, pursue international agreements and risk-reduction measures in space, and establish dialogues with key allies about collective space defense. The bill also requires the Secretary of State to consult with Congress within 90 days of enactment and annually for three years on current and emerging threats to U.S. space security, including information about adversaries' intentions, military capabilities in space, and efforts to prevent hostile actions in orbit. Additionally, the Secretary must notify Congress within 30 days of any significant changes to an adversary's space capabilities or intentions. The legislation contains no specific funding authorization or timeline for implementation beyond the initial congressional consultation requirement.