The period between the two Wars was little more than a staging ground for the second World War, primarily because of the ineptitude of those who negotiated and signed the Treaty of Versailles. Although some attempts were made to prevent another war, such as the Kellogg-Briand Pact and the Washington Naval Armed Conferences, none succeeded, and had no chance of succeeding. Secretary of State Kellogg insisted that all nations sign the Kellogg-Briand Pact as he knew this would render it virtually impotent. Many nations who signed agreements at the Washington Conference abandoned them almost immediately.
At Versailles, France had insisted that Germany be punished and kept weak. The result was harsh treatment of Germany, to the point of unfairness. The German people bitterly resented this, much as the French had resented their own treatment after the Franco-Prussian war. Woodrow Wilson, intent on establishing his League of Nations and providing for an independent Poland with access to the sea did nothing to stop the Polish corridor from cutting directly through an area which was ethnically and culturally German; in fact it separated East Prussia from mainland Germany. Japan had entered World War I expecting territorial gains in Asia, but came away empty handed. Wilson, the consummate White Supremacist, had little interest in the claims of Asians.
Although 'rehearsal" might not be the best description; there is no question that the stage was set for a second conflict in the period between the two wars--a mere twenty years.
I disagree with this statement. There was not yet enough going on during this time to call it a time of rehearsal.
During the 1920s, the world was doing more to try for peace than to prepare for war. Hitler was not yet in power in Germany. Japan had not yet invaded Manchuria. Instead, there were all sorts of attempts at peace going on. There was the Kellogg-Briand Pact. There were the Washington Naval Treaties. All of these things were meant as ways to prevent war.
The real rehearsal for WWII did not come until the 1930s when Japan invaded Manchuria and Hitler came to power and started to build the German military.