The reasons behind the USA's involvement in Vietnam remain a subject of extensive debate. Initially, America supported the French until their defeat at Dien Bien Phu, which then shifted to backing the South Vietnamese government due to fears of communism spreading throughout Southeast Asia.

Why Vietnam delves into the myriad reasons for US involvement, examining theories that date back to 1918 when Woodrow Wilson ignored Ho Chi Minh's plea for independence at the Treaty of Versailles, through to Johnson's full commitment to the undeclared war, which restrained the military to a defensive role in protecting South Vietnam instead of an offensive one that would send troops across the DMZ into Laos and Cambodia.

The questions of why the USA became involved, whether their involvement was justified, and if the war was ever winnable have been fiercely debated for over 50 years. This book seeks to address these 'whys' by providing a thorough examination of all contributing factors, from presidential actions to foreign policy, and the social and political climates of the war era.