No event like a war in human history is literally inevitable. There are all sorts of things that could happen to prevent them. That said, World War II could probably have been prevented somewhat easily. It was less inevitable than some wars have been.
The case for inevitability rests on the attitudes of Germany and Japan. These countries were highly dissatisfied with the status quo of, say, 1930. Because they wanted to expand their power, and because the existing powers wanted to prevent this, war was bound to happen. This is particularly true since this was a time in history when war for the sake of imperialism was still seen as a fairly acceptable thing.
However, the two countries, and Germany in particular, did not need to be upset with the status quo. World War II could likely have been averted simply by ending World War I in a fairer manner. If the Treaty of Versailles had not been so punitive, it is unlikely that Germany would have been as motivated to fight. If the French and British had voluntarily eased the terms of the treaty during the Weimar Republic, the war might not have happened.
We can never know for certain if a war or any other event could have been averted. However, it seems likely that this war could have been.