In my interpretation, the biggest cause of ww2, based on the Munich Conference of September 1938, and Hitlers invasion of Czechoslovakia March 1939, was the Munich Conference --- partly.
This because it proved that weakness in the face of aggression only brought more aggression; giving Hitler Sudetenland (September 1938) was solid ground and power provided for Nazi Germany; which will eventually break its promise (in march 1939) and attack the rest of Czechoslovakia.
What was unknown from the very beginning was that Hitler wanted Europe.
Hitler was looking for expansion he demanded Sudetenland.
He wanted to incorporate this land into the Third Reich and demanded that Prague turn over this land or face war.
Hitler had solid ground he could continue his expansion.
In addition he had the military potential to invade, so the Munich Conference (September 1938) allowed Germany to chop up Czechoslovakia so there will be no war.
Giving Hitler Sudetenland was a graceful beginning as he would later be strong enough to attack the rest of Czechoslovakia.
This was productive to Hitler as he wouldnt need to waste his army and would continue his nazi Germany.
By March 1939 Germany occupied Czechoslovakia. Hitlers objectives were clearly stated. In addition to his power he had military support with Italy, see the Pact of Steel, signed in May (1939), and the Nazi-soviet pact signed in August (1939) with Stallin which he will later break as he did in the Munich agreement.
Hitler was still looking for expansion and ratifying agreements on the right chronology; his opponents faced two choices: 1) Execute Hitlers demands-
2) Or Go to war, and try to stop him
As he invaded Czechoslovakia he not only broke the pact but also was heading for Europes domination, and this by force.
Hitler could not negotiate for equality in power so he could attack all the weak countries as Czechoslovakia to create his empire.
Therefore I come to the conclusion that Hitler would have invaded Czechoslovakia or Sudetenland even if it wasnt given to him, because he had the military power he had support and his purpose was to expand.
Furthermore none of the above causes could be qualified as the biggest cause for ww2; as they both compromise, contributed to Hitlers menace on a second world war.