French declaration of war on Germany (1939) explained

On 3 September 1939—two days after the German invasion of Poland—France declared war on Nazi Germany according to its defensive treaty with Poland, when France's ultimatum to Germany, issued the previous day, expired at 17:00. This occurred hours after the United Kingdom declaration of war on Germany.^{[1] [2]}

See also

• United Kingdom declaration of war on Germany (1939)
• Declarations of war during World War II
• Diplomatic history of World War II

Notes and References

1. Book: Beevor . Antony . The Second World War . 2012 . Little, Brown . 978-0-316-08407-9 . en.
2. Book: Overy . Richard . 1939: Countdown to War . 2010 . Penguin . 978-1-101-50041-5 . en.