Hitler began his quest for Lebensraum, or living space. These steps are what ultimately led to World War 2. He announced Germany's rearmament in 1935, contradicting a main clause in the Treaty of Versailles. Unopposed by other European powers, Germany re-occupied the buffer next to France called the Rhineland, which had been established in the Treaty of Versailles. Still unchallenged, Germany annexed Austria in 1938, and then attacked Czechoslovakia. Pursuing the policy of Appeasement, the other European powers conceded most of Czechoslovakia to Germany at the Munich conference in 1939.
These acts faced little opposition from the other European powers, who were doing everything possible to avoid another Great War. Unrepressed, Hitler finally orchestrated a phony attack by Poland, and used this excuse to declare war. This act finally forced Britain and France to fulfill their treaty obligations to Poland, and the resulting declaration of war, marked the beginning of the Second World War.
It is true that Hitler led Germany through the years preceding and into the Second World War. He carefully manipulated German opinion with extensive propaganda; the cult of personality created to enshrine him as the ultimate leader, cemented his position as German head of state, and guaranteed him control over Germany's actions. His extreme fascist policies enabled Germany's rapid rearmament and ensuing military victories.
It would be too simple to assign all responsibility for WWII to one man, regardless of popular beliefs about his intentions. Hitler was an enabler; his use of propaganda and the available opportunities nearly gave Germany the domination of Europe it desired. Without those circumstances, however, it is unlikely that Hitler would have experienced the same early success towards his goals.
Britain and France had a few chances to stop Hitler, but they didn't. Instead of stopping him, they...