World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier. It involved the vast majority of the world’s nations –including all of the great powers- eventually forming two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. In a state of “total war”, the major participants were not just fighting but throwing their entire economic, industrial, and scientific capabilities behind the war effort. They were not using only military resources, they were also erasing the distinction bewtween civilian and military recourses. Marred by mass deaths of civilians, including the Holocaust and the strategic bombing of industrial and population centres, it resulted in an estimated 50 million to 85 million fatalities. These made World War II the deadliest conflict in human history.

The Empire of Japan aimed to dominate Asia and the Pacific and was already at war with the Republic of China in 1937, but the world war is generally said to have begun on 1 September 1939 with the invasion of Poland by Nazi Germany and subsequent declaration of war on Germany by France and the United Kingdom. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered and controlled much of continental Europe, and formed the Axis Alliance with Italy and Japan. Under the Molotov-Ribbentrop Pact of August 1939, Germany and The Soviet Union partitioned and annexed territories of their European neighbours, Poland, Finland, Romania and the Baltic states. The war continued primarily between the European Axis powers and the coalition of the United Kingdom and the British Commonwealth, with campains including the North Africa and East Africa campaigns, the aerial Battle of Britain, the Blitz bombing campaign, the Balkan Campaign as well as the long-running Battle of the Atlantic. In June 1941, the European Axis powers launched an invasion of The Soviet Union, opening the largest land theatre of war in history, which trapped the major part of the Axis’ military forces into a war of attrition. In December 1941, Japan attacked the United States and European territories in the Pacific Ocean, and quickly conquered much of the Western Pacific.

1) A long action in the past was interrupted by a shorter action (usually expressed in the Simple past).

Examples:
• The guests weren't having dinner when they heard a horrible scream.
• When the murder took place, she wasn’t hiding between the statues.

Notice that, in these cases, the time connector when is used with the simple past and the connector while is used with the past continuous.

2) A long action in the past was taking place or interrupted at a specific time.

Examples:
• She wasn’t hiding between the statues at the time of the murder.
• Last night at 6 pm, I wasn’t eating dinner.

3) Several actions are taking place at the same time in the past (“parallel actions”).

Examples:
• Detective Hercule Poirot wasn’t questioning a witness while Superintendent.
• Sugden was observing the crime scene.
• While Ellen wasn’t reading, Tim was watching the news.

4) Parallel actions in the past continuous are often used to describe the atmosphere of a particular time in the past.

Examples:
• When Hercule Poirot entered the carriage, the passengers weren't waiting for him.
• Two men were sitting stern-faced at the table on the right.
• The woman wasn’t whispering, and the maid wasn’t crying.

Look at the word order in the negative form: