In response to Nazi Germany's invasion of Poland, major Allied nations acted swiftly to combat what they perceived as an existential threat to European peace. France and the United Kingdom were among the first to declare war against Germany on the morning of September 3, 1939, just days after the invasion began on September 1. The United Kingdom's Prime Minister, Neville Chamberlain, made a solemn announcement via radio, highlighting the necessity of standing up against aggression. Following suit, New Zealand and Australia aligned with their British ally as part of the Commonwealth, pledging military support against the Axis forces.

As the declarations of war were formalized, the Viceroy of India, Lord Linlithgow, also announced that India was at war with Germany. However, this was a controversial move as it was executed without seeking the advice or consent of India's provincial legislatures, reflecting the tensions between colonial authority and local governance. This unilateral decision drew criticism from various Indian political factions, who were neither consulted nor represented in this critical decision-making process.

The declarations came amidst a backdrop of rising global tensions following the treaty violations and expansions of Nazi Germany, highlighting the failure of appeasement policies. The onset of these declarations signaled the beginning of widespread mobilization and the eventual escalation into a full-scale global conflict that would engulf many nations over the next several years.