German rearmament began after Hitler left (1932-4) Geneva Disarmament Conference, stating that as the powers would not disarm to his level, he would rearm Germany to their level. By 1935 rearmament was well underway. This involved conscription and munitions factories. Rearmament alarmed the French who, feeling insecure, reinforced the Maginot line (built between 1929 and 1934). This was a line of steel and concrete fortifications stretching from Belgium to Switzerland, Germany would be able to avoid it and invade France via Belgium. France remained passive without Britain’s support. Britain was sympathetic towards Germany and even signed an Anglo German naval Treaty (June 1935) allowing Germany’s navy to be 35% of the size of the Royal Navy. Hitler used his new found arms to support Franco in the Spanish Civil War (1936-9) Hitler sent the Condor Legion of the Luftwaffe to bomb Guernica on 26th April, 1937. Guernica was razed to the ground and Franco went on to conquer the Basque areas of Spain. Hitler had used Spain as a practice ground.
Having broken the Treaty of Versailles once, Hitler risked doing it a second time by marching 30,000 troops into Rhineland on 7th March 1936. France, with 250,000 troops mobilised, remained passive because Britain would not support her. To show that his remilitarization was popular, Hitler held a plebiscite, which showed that 98.8% were in favour. He went on to build his own defensive fortification, the Siegfried Line.
Originally Mussolini did not want to be Hitler’s ally and in 1935 talks were held with Britain and France at the Stresa Front, but these came to nothing when Anthony Eden of Britain threatened oil sanctions against Mussolini during the Abyssinian crisis. This caused the Rome-Berlin Axis in 1936. Mussolini and Hitler strengthened their alliance on two occasions The Anti-Commintern Pact (November 1937) with Japan and The Pact of Steel (May 1939).
September 1938 British Prime Minister, Neville Chamberlain, met German Chancellor Adolf Hitler in Munich to settle the future of the Sudetenland. Hitler's demand that this Czechoslovak land be ceded to Germany was agreed because it was settled by Germans and would therefore be in line with the principle of national self-determination.
Since coming to power in January 1933, Hitler had systematically sought to revise the terms of the Treaty of Versailles which had deprived Germany of territory, and imposed disarmament and reparations. Agreeing to Hitler's demands became known as Appeasement. Appeasement gave Hitler what he wanted with little opposition or objection. They believed that Hitler could be contained if he was given what he wanted within reason. Consequently, this policy of appeasement contributed significantly to the Second World War.
The Sudetenland was lost by Austria in the Treaty of St. Germain (10th September 1919) and hereby Czechoslovakia gained 3 million German speaking people. After the Anschluss the Sudeten German leader, Konrad Henlein, demanded a union with Germany. Unable to receive help from France, the Czech Premier, Benes, mobilised alone. Fearing war, Chamberlain met Hitler on three occasions at Berchtesgaden, Godesburg and at Munich. In the Munich Agreement (29th September, 1938) that was signed by Hitler, Mussolini, Chamberlain and Daladier. It said that Hitler could take the Sudetenland the following day without a plebiscite, that Hungary and Poland could take border districts from Czechoslovakia and that Britain and Germany would never go to war.
In March 1939, Hitler forced Lithuania to give him Memel where most people spoke German. So far Hitler had only taken German speaking territory, so Chamberlain could still appease Hitler. However, in March 1939, Hitler threatened to bomb Prague, so the Czechs surrendered. Chamberlain realised appeasement had failed, so he began to rearm Britain and guarantee peace in Poland.
By the summer of 1939, Hitler’s plans to invade Poland were complete. He realised that to invade Poland might cause Britain to attack him from the West but he was more concerned to avoid a Russian attack from the east. Therefore to avoid a war on two fronts, he arranged the Nazi-Soviet Pact, which said that if either country went to war the other would remain neutral. Hitler gained the chance to invade Poland with a war on one front, if Britain supported Poland. Stalin of USSR gained time to rearm in case Hitler attacked him later, and the chance to gain the eastern half of Poland. This would provide the USSR with a bufferzone.
German tanks invaded West Prussia and Poland on the 1st September 1939 using blitzkrieg tactics. (This is a lightning, sudden attack co-ordinating air, then land forces). Chamberlain sent an ultimatum (a warning with a threat) saying that if Hitler did not withdraw from Poland by 11am, 3rd September 1939, Britain would declare war. On 3rd September, Britain, followed by France, declared war on Germany.
Although it was Hitler’s actions which lead to war, many other factors were important in making the war happen as the ones mentioned above.