All seems lost for the Allies. The Italians are defeated at Caporette, and a Bolshevik Russia pulls out of the war. But the American reinforcements are decisive, and the Allies emerge victorious. The Allies are unable to negotiate an honourable peace agreement, and the Treaty of Versailles, 20 years later, will have disastrous

Carter's dreams of change give way to Ronald Reagan. Gorbachev redeems Reagan and fresh opportunities for peace arise. The debate over Reagan's legacy.

In this bird's-eye view of two continents, demoiselle cranes negotiate a dangerous Himalayan pass on their way to India while high-flying bar-headed geese take the fast track five miles above. In Rajasthan, vultures watch hunting tigers hoping for a meal and pigeons visit a temple dedicated solely to sacred rats. Pigeons are also our guide to the greatest gatherings of camels on Earth and learn to dodge buzzards around the battlements of Jodhpur Fort. 9,000 cranes overwinter in the most unlikely of spots - a barbed wire compound in the centre of a desert town. In Australia, rainbow lorikeets drop in on Sydney and patrol Australia's Gold Coast. In the outback, white cockatoos swirl in thousands and budgerigars pass Uluru (Ayers Rock) and gather in the biggest flocks ever recorded. In China, swallows and swifts visit the Great Wall and the Forbidden City of Beijing. In Japan, the country's most revered birds - Japanese cranes are fed fish by appreciative locals and are joined in strange, momentary harmony by hungry red foxes, white-tailed eagles and Steller's eagles. As peace descends, Japanese cranes dance beautifully in the snow.

Bob Clewell's helicopter crew comes under intense fire in one of the final operations of the war. Joe Galloway returns to Vietnam and in Washington, D.C., Barry Romo throws down his medals in protest. The last American troops return home and POW wife Anne Purcell awaits word of her husband's fate. The fall of Saigon brings the unification of Vietnam.

After more than a century of civil war, Toyotomi Hideyoshi has united Japan. His rivals have either sworn their allegiance, or they have been destroyed. Despite this fledgling peace, Hideyoshi now dreams of a bold and outlandish plan to make himself the most powerful man in Asia. He plans to expand his reign to China. Logistical challenges and fierce operation in Korea prove to be costly.

Morgan Freeman travels the world to study the cycles of war and peace. From the ritualized combat of the sacred Tinku festival in Bolivia to Rwanda's post-genocide reconciliation program, this episode deals with humanity's enormous capacity for violence and the endless pursuit of harmony. Conflict can drive innovation, but is war necessary?