One of the more striking things about Anne Franks diary is how, for a very young girl, she seems so mature and wise. Maybe it's the contrast with the hardships and cruelties of wartime Holland taking place around her family's hiding place.
When she places equal blame on "the little man" for the start of World War II, she is talking about the average citizen of Germany, France or Britain who elected and often supported leaders who would allow such a catastrophe to happen. Mostly, she is talking about the German people, who elected Nazis to power in the Reichstag, and did little to oppose Hitler's war or the Holocaust against the Jews.
It's one of the moments in the book, one of many, where she seems wise beyond her years, and one of the reasons why her diary in particular is still so widely read and taught.