Rearmament among the nations that would eventually be the major combatants in WWII was begun before 1930. Russia, Japan, Germany, France, the UK, Italy, and in a minor way the US were all entering arms races with their neighbors. Each had taken lessons from how WWI was conducted and wanted to win the next war by applying those lessons. This was begun before Hitler took power.

Now, rearmament doesn't necessarily mean war was inevitable, but it is a clear indication of raised tensions in a region. The instigators of WWII--Germany (with Italy following behind) and Japan--were the match that lit the tinder that was laid by rearmament. People made decisions to wage aggressive war. Those choices could have gone differently. Given the personalities in question it is unlikely, but it still wasn't inevitable. It also wasn't a total surprise. When neighboring nations build up their capabilities over the span of a decade it's not a shock when those armaments are used. One example of how WWII wasn't a surprise was the case of the Republicans during the Spanish Civil War, who desired to delay their defeat as long as possible so that when war broke out they would get aid from France and the UK during the war the Republicans were sure would break out very soon. For them it didn't happen soon enough, as they surrendered in April 1939 and and WWII broke out in Europe that fall.

For the rationale behind interwar rearmament, Maiolo's Cry Havoc is excellent.

By about 1939, WWII was certainly seen as inevitable. Germany had long since been rearming, while France and Britain were doing the same essentially from the Munich Crisis (1938) onwards. After Hitler occupied the Czechlands in 1939, it was clear that he could not be expected to keep his word. Once Poland was in his sights, despite efforts to arrive at a treaty, conflict was really only a matter of time.