World War Two was not caused solely by short term events in the 1930's such as Austria and Czechoslovakia. The anger and resentment that built up in Nazi Germany - and which was played on by Hitler during his rise to power and when he became Chancellor in January 1933 - also had long term causes that went back to the 1919 Treaty of Versailles. Patriotic Germans had never forgotten their nation's treatment in Paris in that year.
The League had some successes in this decade (the Aaland Islands, as an example) but the weaknesses of the League had also been cruelly exposed on a number of occasions when an aggressor nation successfully used force to get what it wanted and the League could do nothing. This process set the mould for the 1930’s and any would-be dictator would have been very well aware that the League did not have the ability to enforce its decisions as it lacked an army. Those nations that were best equipped to provide the League with a military force (Britain and France) were also not prepared to do so for domestic reasons and the aftermath of the Great War in which so many were killed or wounded. From a political point of view, the British and French publics would not have tolerated a military involvement in an area of Europe that no-one had heard of. Politicians were responsive to the attitudes of the voters and neither Britain nor France were prepared to militarily support the League in the 1920’s - despite being the strongest nations in the League.
However, the apparent stability in Europe after 1925 and its apparent prosperity, meant that conflicts rarely occurred from 1925 to 1929.
In fact, Europe could have been confident in assuming peace would last as two treaties were signed that seemed to indicate that a new era of peace and toleration had been ushered in.
The Locarno Treaties were signed in December 1925. The major politicians of Europe met in neutral Switzerland. The following was agreed to :
France, Germany and Belgium agreed to accept their borders as were stated in the Treaty of Versailles. France and Belgium would never repeat an invasion of the Ruhr and Germany would never attack Belgium or France again. Britain and Italy agreed to police this part of the treaties. Germany also accepted that the Rhineland must remain demilitarised. In other treaties, France promised to protect Belgium, Poland and Czechoslovakia if Germany attacked any one of them. Germany, Britain, France, Italy, Belgium, Poland and Czechoslovakia all agreed that they would never fight if they had an argument between themselves - they would allow the League to sort out the problem.
However, nationalists in Germany were furious with their government for signing these treaties. By signing, the German government effectively agreed that it accepted the terms of the Versailles Treaty of 1919. This to the nationalists bordered on treason and was totally unacceptable. Their claims of treason went unheard as Weimar Germany was experiencing an economic growth and the hard times of 1919 to 1924 were forgotten. Moderate politicians were the order of the day in Germany and the extreme nationalists such as the Nazi Party faded into the background. The success of these moderate politicians was emphasised when France backed Germany’s right to join the League of Nations which Germany duly did in 1926.
The other major treaty which seemed to herald in an era of world peace was the Kellogg-Briand Pact of 1928.
This pact was signed by 65 countries. All 65 nations agreed never to use war again as a way of solving disputes.
Therefore, Europe was effectively lulled into a false sense of security by 1929 as the politicians of Europe had made it plain that war was no longer an option in solving disputes and that previous enemies were now friends. This new Europe relied on nations being at peace and harmony with one another. The stability of Germany was shattered by the Wall Street Crash of October 1929 and the nationalists who had spent 1925 to 1929 in relative obscurity, rose to the political surface once again. They had no intention of accepting either Versailles or the Locarno treaties and the League’s weaknesses in this decade had also become apparent. The League could only function successfully, if the politicians of Europe allowed it to do so. Hitler and the Nazis were never going to give the League a chance once they had gained power.