Conversation so far:
when did world war 2 start and end
The Second World War started on 1 September 1939 and ended on 2 September 1945.
what happened on 1 September 1939 in world war 2
The Second World War started on 1 September 1939 with Hitler's invasion of Poland.

Question: how long did the war last
Self-contained rewrite: how long did world war 2 last