1940s

1940:

March: The Katyn Forest Massacre. Yevgeny Borisovitch Volgin takes part in the massacre.

1941:

June 22nd: Nazi Germany invades the Soviet Union.

July: The Special Air Service of the British army is formed. Their motto, "Who Dares, Wins", is a tribute to The Boss.

December 7th: The Imperial Japanese Navy attacks Pearl Harbor. The United States declares war on Japan.

December 9th: Adolf Hitler declares war on the United States of America.

1942:

June 13th: The Office of Strategic Services is opened.

August: The Manhattan Project begins. Otacon's grandfather is assigned to work on the project.

August 21st: The German army besiege the city of Stalingrad (now Volgograd).

December 2nd: Physicist Enrico Fermi splits an atom in a nuclear reactor, generating the first artificial nuclear fission chain reaction.

The Boss forms the Cobra Unit in Stalingrad, an elite unit that plays a pivotal role in key Allied victories during the darkest days of World War II.

1943:

February 2nd: The Battle of Stalingrad ends with a Soviet victory.

1944:

June 6th (D-Day): The Allied Forces dispatch the Cobra Unit into Normandy. The Cobra Unit partakes in a mission to take down V2 Missile Installations. The Boss gives birth to Ocelot; The Sorrow is the father. The baby is eventually taken by The Philosophers.

June 11th: USS Missouri commissioned.

1945:

April 30th: The Red Army advances on Berlin. Adolf Hitler commits suicide.

May 8th: Berlin falls to the Red Army. Germany surrenders; the Nazi party is abolished.

July 16th: The first nuclear test, code-named "Trinity", is conducted in Alamogordo.

August 6th: Hiroshima is bombed. Otacon's father is born.

August 9th: Nagasaki is bombed.

August 15th: Japan surrenders. World War II ends; the Cold War begins.

September 2nd: Vietnam declares independence.

1946:

February 14th: ENIAC, the world's first electronic computer, is unveiled.

1947:

May 3rd: Japan enacts Article 9 of the Japanese Constitution to renounce war, as well as being unable to maintain an army.

September: The Central Intelligence Agency is created.

October 14th: Pilot Chuck Yeager breaks the sound barrier in the Bell X1.

The Boss disbands the Cobra Unit.

1948:

March 12th to April 24th: The Costa Rican Civil War. A rebel army under commander José Figueres leads an armed uprising against the Costa Rican government, which it quickly defeats. Paz Ortega Andrade's grandparents were killed during the war.

December 1st: José Figueres's provisional junta abolishes the Costa Rican army, becoming a "nation without a military".

1949:

April 4th: NATO is formed.

May: Germany is split up into East and West Germany.

August: The USSR tests their first nuclear bomb in Semipalatinsk, Kazakhstan, and becomes the world's second nuclear power.

October 1st: The Chinese Civil War ends in a Communist victory. The People's Republic of China is formed.

December 13th: Israel forms the Mossad.