This whitepaper examines the integration of Zero Trust Architecture (ZTA) and Cross Domain Solutions (CDS) to secure multilevel cyberspace for government and defense. CDS enables secure data flow and access between isolated networks, while Zero Trust enforces identity, device, and data-centric security. Together, they address challenges like insider threats, multilevel data consolidation, and compliance with federal mandates, ensuring a robust, scalable framework for protecting sensitive systems and fostering secure digital transformation.