World War II started in 1939 and ended in 1945.
Specific dates:
Start: September 1, 1939 — Germany invaded Poland. Britain and France declared war on Germany two days later, on September 3, 1939.
End: September 2, 1945 — Japan formally surrendered aboard the USS Missouri, ending the war completely.
But "start and end" isn't as clean as one date on each side. Here's why:
Why the start date is debated:
The 1939 date is the standard Western answer, tied to the invasion of Poland.
Many historians argue the war effectively began earlier in Asia:
Japan invaded Manchuria in 1931.
Japan launched a full-scale war against China in July 1937.
If you use the Asian starting point, WWII lasted closer to 14 years, not 6.
China's official position, and increasingly that of many historians, treats 1937 as the real start of the war, since it was already a large-scale, sustained conflict involving millions of troops and massive civilian casualties — not a border skirmish.
Why the end date also isn't a single moment:
May 8, 1945 (V-E Day) — Germany surrendered, ending the war in Europe.
August 6 and 9, 1945 — The US dropped atomic bombs on Hiroshima and Nagasaki.
August 15, 1945 (V-J Day) — Japan announced its surrender.
September 2, 1945 — The formal surrender document was signed, marking the legal end of the war.
So even the "end" has at least three defensible dates depending on what you're measuring: military defeat, public announcement, or formal legal surrender.
Why this matters if you're using this fact for something:
If you're writing something academic or precise, saying "1939–1945" without qualification is fine for the European theater but incomplete for the global war.
If the context is China, Japan, or broader Asian history, citing only 1939 will look like an oversight, since it ignores 8 years of war already underway.
If you're citing casualty figures, GDP losses, or military campaigns "during WWII," check whether the source uses the 1937 or 1939 starting point — this changes the numbers substantially.
Quick reference table:
Event | Date |
|---|---|
Japan invades Manchuria | 1931 |
Japan invades China (full-scale) | 1937 |
Germany invades Poland | Sept 1, 1939 |
Britain/France declare war | Sept 3, 1939 |
Germany surrenders (V-E Day) | May 8, 1945 |
Atomic bombs dropped | Aug 6 & 9, 1945 |
Japan announces surrender (V-J Day) | Aug 15, 1945 |
Formal surrender signed | Sept 2, 1945 |