- March 12th - Finland signs peace treaty with Soviet Union.
- April 9th - Germany begins occupation of Denmark and invades Norway.
- May 10th - Germany invades Belgium, Holland and Luxembourg.
- May 10th - British Prime Minister, Chamberlain, resigns, replaced by Churchill.
- May 15th - Holland surrenders to Germany.
- May 26th - Evacuation of British Expeditionary Force from Dunkirk.
- May 27th - Belgium surrenders to Germany.
- June 10th - Capitulation of Norway.
- June 10th - Italy declares war on Britain and France.
- June 14th - German army enters Paris.
- June 18th - Soviets invade Baltic states.
- June 22nd - France signs armistice with Germany.
- June 30th - Germany begins occupation of Channel Islands.
- July 10th - Start of Battle of Britain.
- July 11th - Petain becomes head of French Vichy Government.
- August 3rd - Italy begins occupation of British Somaliland.
- September 13th - Italy invades Egypt.
- September 27th - Germany, Italy and Japan sign Tripartite Pact.
- October 7th - German army moves into Rumania.
- October 28th - Italy invades Greece.
- November 14th - Greek army repels Italians back into Albania.
- November 22nd - Italian 9th Army defeated by Greeks.
- December 11th - British capture Sidi Barrani, Egypt, from Italians.
- December 17th - British recapture Sollum, Egypt.