Final answer:
The Pentagon officially recognizes Cyber as the fifth domain of warfare, which accompanies the previously known domains of land, air, and sea. This is part of a broader evolution towards hybrid warfare where various elements including technology and cyberspace are integrated into military strategy.
Step-by-step explanation:
The fifth domain of warfare that the Pentagon officially recognizes, in addition to land, air, and sea, is Cyber (D). This aligns with the concept of hybrid warfare, which refers to a blend of conflicts across multiple fronts simultaneously, including political, conventional, irregular, and cyberwarfare. The rise of technology has allowed militaries to engage in combat through different means such as drones and advanced long-range missile systems and to weaponize information technology and cyberspace, introducing a new dimension to military strategy.