Cadeyrn said:
I think the actuall cause of the war (the european one anyway) dates back to 28.06.1919. After that humilating 'treaty' it wasn't really the question if a second war would come, but when. It's my believe that all this could have been prevented by a resonable conclusion of ww1.
Even further back for the Japanese... While Japan was dedicated to building an empire from the late 19th century there seems to have been a major change in attitude after the sino-japanese war (1894-95). When it became clear that the european powers were willing to deny Japanese expansion through coordinated action. Like Germany, Japan was revisionist in the sense that they felt they had been 'cheated' of their status as an imperial power.
Interestingly Versailles cemented this feeling when the Japanese proposed a racial equality clause and were unceremoniously turned down by everybody, especially the americans.
If you ask me (and nobody ever does

) the cause of the world wars was the late 19th century creation of several new and reasonably powerful states which had been convinced by the british and french examples that the imperial model was the route to security and prosperity. They were trying to sieze 'a place in the sun' at about the same time that the existing imperial / colonial powers were realising that their position was un-sustainable and that imperialism had gone too far.