Thirty-five years ago, Sir John Hackett published The Third World War, which speculated how WW3 might start and how it would be fought. Since it is now fashionable to call WW3 the Cold War, the time is right to publish a book about WW4, how it might start and most likely be fought. War planners must envision the unexpected and plan for the improbable, and the 20th century’s theories of total war are going to be rendered obsolete by the 21st century’s nuclear-enforced concept of limited war. In the future, with mutual acceptance of national survival in place, Mutually Assured Survival (MAS) wars will be waged between nuclear powers without introducing nuclear weapons. This is the possible future in nine scenarios: ·The Post-NATO War: It will begin between allies, not enemies, in seemingly unconnected events. ·The Great Russian War: Russia will seek to reverse its loss of empire through its version of Manifest Destiny. ·The Great China War: By embracing capitalism in an authoritarian command-control economy, China supplanted communism with a form of expansionist fascism. ·The Chinese Civil War: Chinese fascism will become a victim of rising expectations and diminishing realities. ·The Polar War: Another resource rush is on, and as 500 years ago, a treaty allocating sovereignty was made to be broken. ·The Blue Gold War: Diminishing fresh water will spawn conflicts of desperation. ·The Lunar War: The Moon will come to be coveted as the only permanent low-gravity satellite. ·The Nuclear Terrorist War: As the Taliban, al Qaeda, and ISIS terrorists inch closer in connection and proximity to sympathetic extremists in Pakistan, that nation’s nuclear arsenal is increasingly likely to fall into their hands. ·The Commerce, Currency, and Cyber War: With globalization, government-sanctioned predatory trade practices, cyber-based industrial espionage, currency manipulation, and other financially provocative actions will lead to war. Human folly is the great imponderable. Yet, does folly upset the calm or is the storm the natural state in the sea of humanity? Either way, folly or nature ensures a future filled with conflict.