Today, 3 September 2020, marks 81 years since Britain's entry into the Second World War.
By 1939, much of the world had returned to peace following the horrors of World War One, more than 20 years previously.
With the end of the Great War, there was also great damage across Europe - 17 million people were killed, homes were lost and people's livelihoods ruined.
Germany was perhaps the most affected - the signing of the Treaty of Versailles in June 1919 saw them take the blame for starting the war.
As a result, they were punished with huge fines, their military was shrunk to a fraction of its size and 13% of its territory, including east Prussia and Alsace-Lorraine, was removed.
Germany's economy was crippled post-World War One and many were furious with the country's government for agreeing to the terms of the treaty.
This instability and anger opened the door for Adolf Hitler, who wanted to claim back land Germany had lost, take control of Europe and ultimately reverse the terms agreed to in the Treaty of Versailles.
The Beginning Of War
By 1939, the Nazis had made huge strides in their aim of making Germany a world power.
Hitler had already violated many of the agreements signed in the Treaty of Versailles, including the rebuilding of Germany's military and the remilitarisation of the Rhineland.
Britain was one of the nations that signed the treaty but also played a role in allowing Germany to return as a European powerhouse.
During the mass rearmament of Nazi Germany in the 1930s, Britain agreed to a policy of appeasement - allowing Hitler to expand German territory.
In 1938, German troops annexed Austria, followed by the UK, France and Italy all agreeing to Germany occupying the Sudetenland, a part of German-speaking Czechoslovakia.
The UK decided to allow Germany's occupation to prevent the possibility of war - the British people were happy as they did not want another conflict and the UK simply could not afford mass rearmament.
However, not everyone was impressed - Winston Churchill (who was not yet prime minister) said the appeasement policy was "an unmitigated disaster".
Less than a year later on 1 September 1939, Germany invaded Poland and World War Two was imminent.
Britain and France ordered Germany to remove its troops from Poland and when Germany refused, as part of the Anglo-Polish pact, the two nations declared war just two days later.
The UK immediately deployed the British Expeditionary Army to France over fears of a German invasion.
For years before the war, Germany had rearmed and restrengthened its military greatly, something the UK had not.
However, the UK had invested in the RAF - both the Hurricane and Spitfire were brought into service before the outbreak of war and proved key in the UK's Battle of Britain win.
On the other hand, the UK realised its army was too small and in April 1939, amid the threat of Nazi Germany, the conscription law was introduced.
All fit and able British men aged 20-21 were required to train with the military for six months, but when war broke out, the British Army was still much smaller (879,000 personnel) than Germany's and allies like France.
A subsequent act was introduced to boost the numbers further, meaning all men aged 18-41 could be called up.
By the end of 1939, more than 1.5 million extra personnel had been conscripted into the British military with around 1.1 million going to the Army and the rest split between the Navy and RAF.
Key Moments Involving Britain During World War Two
- 3 September 1939: UK and France declare war on Germany
- 10 May 1940: Winston Churchill becomes Prime Minister
- 10 May 1940: Germany invades Western Europe
- 14 May 1940: The Home Guard was created (then named Local Defence Volunteers), made up of those ineligible for frontline service
- 26 May - 4 June 1940: More than 350,000 British and French troops were evacuated from the beaches of Dunkirk, France
- 10 June 1940: Italy declared war on Britain and France
- June 1940: German forces invade the Channel Islands before beginning occupation of the islands
- 10 July - 31 October 1940: The Battle of Britain begins
- 7 September 1940: The Blitz begins
- 22 June 1941: 'Grand Alliance' formed between the UK, the US and Soviet Union
- 7 December 1941: Japan attacks American Naval Base at Pearl Harbour
- 8 December 1941: US declares war on Japan and sides with the Allies
- 6 June 1944 - D-Day: British and US troops land on the beaches of northern France to push German troops back
- 25 August 1944: Allied troops liberate Paris
- 16 December 1944 - 25 January 1945: The Battle of the Bulge - the last major Nazi offensive of WWII
- 8 May 1945: Germany surrendered, known as VE Day (Victory in Europe Day)
- 9 May 1945: German occupation of the Channel Islands officially ends, with signing of the Instrument of Surrender
- 15 August 1945: Japan surrendered, known as VJ day (Victory in Japan Day)
- 2 September 1945: official end of World War Two
Political Changes In The UK
Neville Chamberlain, Britain's prime minister during the policy of appeasement, was replaced by Winston Churchill on 10 May 1940.
On the morning of Mr Churchill's appointment, Germany had just invaded France, Belgium, the Netherlands and Luxembourg - closing in on Britain.
The appointment of Mr Churchill saw a shift in military strategy for Britain and also an eventual change in fortunes.
Mr Churchill was very popular and was an inspiration to many - his speeches rallied people behind the war effort during some of the most testing times, including the Battle of Britain and the Blitz.
"We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender," an extract from one of Mr Churchill's most famous speeches, We Shall Fight On The Beaches, in June 1940.
However, some historians argue his greatest achievement during World War Two was creating the 'Grand Alliance'.
In June 1941, he persuaded both the United States and the Soviet Union to side with Britain and form the 'Grand Alliance'.
There were pre-existing tensions between the countries, in particular the US and the Soviet Union, but the move by Mr Churchill has since been seen as a turning point in the war.
However, the US did not officially enter the war until the day after the attack on Pearl Harbour.
Despite playing a major part in winning the war, Mr Churchill's time in office soon came to an end.
In July 1945, the Conservative Party lost a general election in a landslide victory for Labour.
Mr Churchill and the Tories were not seen as the people needed to rebuild a broken Britain.
Instead, the people wanted a more socialist government and Clement Attlee replaced Churchill at Number 10.
Mr Attlee oversaw the introduction of the National Health Service (NHS) and the nationalisation of the coal mining and steel industry.
In 1951, Mr Churchill was re-elected as prime minister at the age of 77.
He was knighted in 1953 and retired two years later over health concerns.
The Cost Of World War Two
World War Two lasted around six years and the price of human life was huge.
It proved to be the deadliest conflict in history - some estimates say as many as 85 million people were killed.
Statistics from the National WWII Museum in New Orleans show the number of soldiers and civilians killed from some of the Allied Powers:
- United Kingdom - 450,700
- France - 567,600
- Australia - 40,500
- Poland - 5,600,000
- Greece - 300,000-800,000
- The Netherlands - 301,000
- United States - 418,500
- Soviet Union - 24,000,000
The Axis Powers also suffered large losses:
- Germany - 6,600,000-8,800,000
- Japan - 2,600,000-3,100,000
- Hungary - 560,000
- Italy - 457,000
- Romania - 833,000
- Bulgaria - 25,000
It is believed around 3% of the world's total population was killed during the Second World War.
According to figures released by the BBC, 144,000 British Army soldiers, 70,000 RAF personnel and 50,000 Royal Navy sailors were killed in the conflict.
Cover image: Royal Marines off a Normandy Beach on D-Day, 6 June 1944 (Picture: PA).