Key European points in the Second World War
Part 1
Starting with events prior to the beginning of the Second World War, continuing with the war prior to the Soviet Union joining the Allied Forces.
An event that was forced upon the Soviet Union because of the German invasion of Russia known as Operation Barbarossa an event that ended the Molotov–Ribbentrop Pact.
September 1938 – Munich AgreementThe Munich Pact was an agreement permitting the Nazi German annexation of Czechoslovakia's Sudetenland. The Sudetenland were areas along Czech borders, mainly inhabited by ethnic Germans. The agreement was negotiated at a conference held in Munich, Germany, among the major powers of Europe without the presence of Czechoslovakia. Today, it is widely regarded as a failed act of appeasement toward Nazi Germany.
Another view is that he Munich pact gave Nazi Germany a defacto license to operate as they wished in Eastern Europe.
August 1939 – Molotov–Ribbentrop PactThe Molotov–Ribbentrop Pact, colloquially named after the Soviet foreign minister Vyacheslav Molotov and the German foreign minister Joachim von Ribbentrop, was an agreement officially titled the Treaty of Non-Aggression between Germany and the Soviet Union[1] and signed in Moscow in the late hours of 23 August 1939.[2] It was a non-aggression pact under which the Soviet Union and Nazi Germany each pledged to remain neutral in the event that either nation were attacked by a third party. It remained in effect until 22 June 1941, when Germany invaded the Soviet Union.
In addition to stipulations of non-aggression, the treaty included a secret protocol dividing Northern and Eastern Europe into German and Soviet spheres of influence, anticipating potential "territorial and political rearrangements" of these countries. Thereafter, Germany and the Soviet Union invaded, on September 1 and 17 respectively, their respective sides of Poland, dividing the country between them.

Part of eastern Finland was annexed by the Soviet Union after the Winter War. This was followed by Soviet annexations of Estonia, Latvia, Lithuania, Bessarabia, Northern Bukovina and Hertza region.
(More on the Molotov–Ribbentrop Pact in the first post on this thread).
September 1939 – The Invasion of PolandThe Invasion of Poland, also known as the September Campaign or 1939 Defensive War, was an invasion of Poland by Germany, the Soviet Union, and a small Slovak contingent that marked the start of World War II in Europe. The invasion began on 1 September 1939, one week after the signing of the Molotov–Ribbentrop Pact, and ended on 6 October 1939 with Germany and the Soviet Union dividing and annexing the whole of Poland.
November 1939.-.March 1940 - The Winter War
The Winter War was a military conflict between the Soviet Union and Finland. It began with a Soviet offensive on 30 November 1939 — three months after the start of World War II and the Soviet invasion of Poland — and ended on 13 March 1940 with the Moscow Peace Treaty.
The League of Nations deemed the attack illegal and expelled the Soviet Union from the League on 14 December 1939.
The Soviet forces had three times as many soldiers as the Finns, 30 times as many aircraft, and a hundred times as many tanks.
The Red Army, however, had been crippled by Soviet leader Joseph Stalin's Great Purge of 1937, reducing the army's morale and efficiency shortly before the outbreak of the fighting. With more than 30,000 of its army officers executed or imprisoned, including most of those of the highest ranks, the Red Army in 1939 had many inexperienced senior officers. Because of these factors, and high commitment and morale in the Finnish forces, Finland was able to resist the Soviet invasion for far longer than the Soviets expected.
Hostilities ceased in March 1940 with the signing of the Moscow Peace Treaty. Finland ceded 11% of its pre-war territory and 30% of its economic assets to the Soviet Union. Soviet losses on the front were heavy, and the country's international reputation suffered. The Soviet forces did not accomplish their objective of the total conquest of Finland, but did gain sufficient territory along Lake Ladoga to provide a buffer for Leningrad. The Finns, however, retained their sovereignty and enhanced their international reputation.
The peace treaty thwarted the Franco-British plan to send troops to Finland through northern Scandinavia. One of the Allied operation's major goals had been to take control of northern Sweden's iron ore and cut its deliveries to Germany.
May 1940
Germany turns westward with the occupation of the Low Lands and then France
The evolution of German plans for Fall Gelb, the invasion of the Low Countries.
The series begins at the left upper corner. The British Expeditionary Force and the subsequent evacuations after the collapse of France. The(BEF) was the name given to the British Forces in Europe from 1939–1940 during The Second World War. Commanded by General Lord Gort, the BEF constituted 1⁄10 of the defending Allied force.
The British Expeditionary Force was started in 1938 in readiness for a perceived threat of war after Germany annexed Austria in March 1938 and the claims on the Sudetenland which led to the invasion of Czechoslovakia in March 1939. After the French and British had promised to defend Poland the German invasion began and war was declared on 3 September 1939.
The BEF was sent to France in September 1939 and deployed mainly along the Belgian—French border during the so called
Phoney War leading up to May 1940. The BEF did not commence hostilities until the invasion of France on 10 May 1940. After the commencement of battle they were driven back through France forcing their eventual evacuation from several ports along the French northern coastline in Operations
Dynamo,
Ariel and
Cycle. The most notable evacuation was from the Dunkirk region and from this the phrase Dunkirk Spirit was coined.
26 May .-. 3 June 1940 The Dunkirk evacuation, known also as Operation Dynamo.
The Dunkirk evacuation, code-named Operation Dynamo by the British, was the evacuation of Allied soldiers from the beaches and harbour of Dunkirk, France, between 26 May and the early hours of 3 June 1940, when British, French and Belgian troops were cut off by the German army during the Battle of Dunkirk in the Second World War.
The evacuation was ordered on 26 May. In a speech to the House of Commons, Winston Churchill called the events in France "a colossal military disaster", saying that "the whole root and core and brain of the British Army" had been stranded at Dunkirk and seemed about to perish or be captured. In his ("We shall fight on the beaches") speech, he hailed their rescue as a "miracle of deliverance".
On the first day, only 7,011 men were evacuated, but by the ninth day, a total of 338,226 soldiers (198,229 British and 139,997 French) had been rescued by the hastily assembled fleet of 850 boats. Many of the troops were able to embark from the harbour's protective mole onto 42 British destroyers and other large ships, while others had to wade from the beaches toward the ships, waiting for hours to board, shoulder-deep in water.

Others were ferried from the beaches to the larger ships, and thousands were carried back to Britain by the famous "little ships of Dunkirk", a flotilla of around 700 merchant marine boats, fishing boats, pleasure craft and Royal National Lifeboat Institution lifeboats — the smallest of which was the 15 ft (4.6 m) fishing boat Tamzine, now in the Imperial War Museum — whose civilian crews were called into service for the emergency.
The "miracle of the little ships" remains a prominent folk memory in Britain.
It can be argued that allowing the Allied troops to escape back to Britain was the first error of military judgement made by the German military command.
The rescue of the British troops at Dunkirk provided a psychological boost to British morale; to the country at large it was spun as a major victory. While the British Army had lost a great deal of its equipment and vehicles in France, it still had most of its soldiers and was able to assign them to the defence of Britain. Once the threat of invasion receded, they were transferred overseas to the Middle East and other theatres and also provided the nucleus of the army that returned to France in 1944.
German land forces could have easily destroyed the British Expeditionary Force, especially when many of the British troops, in their haste to withdraw, had left behind their heavy equipment. For years, it was assumed that Adolf Hitler ordered the German Army to stop the attack, favouring bombardment by the Luftwaffe. However, according to the Official War Diary of Army Group A, Feldmarshall Gerd von Rundstedt, the Chief of the General Staff, ordered the halt. Hitler merely validated the order several hours after the fact. This lull in the action gave the British a few days to evacuate by sea.
Several high-ranking German commanders (for example, Generals Erich von Manstein and Heinz Guderian, as well as Admiral Karl Dönitz) considered the failure of the German High Command to order a timely assault on Dunkirk to eliminate the British Expeditionary Force to be one of the major mistakes the Germans had made on the Western Front.

It is to be remembered that Britain is an Island and therefore relies on the Royal Navy (the Senior Service) for it's defence more than it depends on an Army.
Admittedly the troops that were evacuated left most of their equipment behind on the beaches (after rendering the equipment useless) but it was the manpower that was more important than the materiel.
Materiel can be replaced with some difficulty during the shortages caused by the war but it would have been impossible to replace the troops.