An era of good feeling in European international relations witnesses major agreements that ease reparations (the Dawes Plan, 1924 and the Young Plan, 1929) and guarantee frontiers (the Locarno Treaties, 1925). Germany is admitted to the League of Nations (1926).
Stalin defeats the last of his major rivals for power in the period after Lenin's death (Jan. 1924). Over time Stalin's ascendancy brings forced industrialization, brutal police repression and purges, a deeply suspicious attitude toward the outside world, and rigid control over foreign Communist parties.
The American stock market crash starts a world-wide Depression, which is at its worst in most of Europe from the summer of 1931 through the end of 1932 and in some places much longer.
Japanese armies open a long undeclared war against China in Manchuria. Attempts to restrain Japan through the League of Nations or by other means all fail, weakening faith in the international order.
Hitler becomes Chancellor of Germany. He and his Nazi party are in full command in a matter of months.
The Third Reich withdraws from the disarmament conference and the League of Nations.
This agreement, Hitler's first significant initiative in Eastern Europe, weakens the French policy of security alliances against Germany.
Soviet Russia finally joins the League of Nations out of concern about the threat from Nazi Germany.
The Third Reich repudiates the disarmament clauses of the Treaty of Versailles and begins to rearm openly.
During the international crisis over Italy's invasion of Abyssinia (Ethiopia), all attempts by the League and other forums to agree on effective action to restrain Italy fail. "Collective security" under the League loses much of its remaining credibility. Hitler's support of Mussolini's war brings Germany and Italy into alliance.
Nazi Germany repudiates the demilitarization clauses of the Treaty of Versailles and the Locarno Treaties and sends troops into her western territories (the Rhineland).
A civil war breaks out in Spain, lasting until 1939. Germany and Italy support the insurgent Nationalist side (Franco) and send arms and "volunteers"; Britain, France, and Russia support the Republican government but only Russia provides any practical assistance.
The Anti-Comintern Pact loosely connects Germany to Japan and Italy.
Germany annexes Austria after a sudden crisis
A crisis over a large border region in western Czechoslovakia (the so-called "Sudetenland") ends in the Munich agreement between Germany, Britain, France, and Italy, which authorizes German annexation of these territories.
Germany suddenly occupies the rest of western Czechoslovakia and turns Slovakia into a separate client state. This brings the final disillusionment to most British and French "appeasers" who had hoped for a stable settlement with Germany.
Hitler would renounce the agreement, no longer willing to adhere to any limitations at all per the WWI treaty, as Germany was poised for a renewed conflict.
Germany's invasion of Poland is followed by British and French declarations of war on Germany. The Soviet Union, having signed the Nazi-Soviet Pact with Germany a week earlier, remains out of the war and in fact uses the terms of the Pact to justify its occupation of part of Poland, the Baltic States, and parts of Romania over the next year.