describe a significant historical event that occurred during author's life that may have had an influence upon her writing.

Certainly WW2 as a whole was the reason Anne and here family were in hiding. I think an event in particular might be the D-Day invasion that influenced her writing. She found new purpose and vigour in her writings as a historical document. Check out this quote from entry (6th June, 1944) :

"This is D-day", came the announcement over the British radio. The invasion has begun! According to the German news, British parachute troops have landed on the French coast. British landing craft are in battle with the German Navy, says the BBC....

"Great commotion in the 'Secret Annexe'! Would the long-awaited liberation that has been talked of so much but which still seems too wonderful, too much like a fairy-tale, ever come true? Could we be granted victory this year, 1944? We don't know yet, but hope is revived within us; it gives us fresh courage, and makes us strong again."