Here is a list of important dates in the development of the English language. The selection of events is my own, and the dates are approximate in some cases, but it gives at least some idea of the time-scales involved, and puts the developments into some sort of perspective.
Britain cut off from continental Europe by English Channel
Proto-Indo-Europeans living in Eastern Europe and Central Asia
Germanic Indo-European tribes living in parts of modern-day Germany
Celts inhabit much of Europe, and beginning to colonize the British Isles
First Roman raids on Britain under Julius Caesar
Roman occupation of Britain under Emperor Claudius (beginning of Roman rule of Britain)
Roman withdrawal from Britain
Anglo-Saxon settlement (Angles, Frisians, Saxons, Jutes) of Britain begins
Earliest Old English inscriptions
St. Augustine arrives in Britain (beginning of Christian conversion of the Anglo-Saxons)
Anglo-Saxon language covers most of modern-day England
“Cædmon’s Hymn” composed in Old English
The Venerable Bede writes “The Ecclesiastical History of the English People” (in Latin)
Viking raids of Britain begin
Old English epic poem “Beowulf” composed
The Danes launch full-scale invasion and occupy Northumbria
Alfred the Great becomes king of Wessex, encourages English prose and translation of Latin works
“The Anglo-Saxon Chronicle” is begun
Danelaw established, dividing Britain into Anglo-Saxon south and Danish north
Charles II of France grants Normandy to the Viking chief Hrolf the Ganger (the beginning of Norman French)
The oldest surviving manuscript of “Beowulf” dates from this period
The Norman conquest under William the Conqueror
London becomes de facto capital of England
The oldest surviving manuscripts in Middle English date from this period
Eleanor of Aquitaine, French wife of Henry II, becomes Queen Consort of England
“The Anglo-Saxon Chronicle” discontinued
Oxford University established
The “Ormulum” text of the monk Orm completed
King John loses the province of Normandy to France
Cambridge University established
The Black Death kills one third of the British population
The Statute of Pleading replaces French with English as the language of law (although records continue to be kept in Latin)
English is used in English Parliament for the first time
William Langland writes “Piers Plowman”
John Wycliffe publishes his English translation of “The Bible”
English replaces Latin as main language in schools (except Universities of Oxford and Cambridge)
Chaucer begins “The Canterbury Tales”
Henry IV becomes first English-speaking monarch since before the Conquest
The Great Vowel Shift begins
William Caxton establishes the first English printing press
Start of English Renaissance
William Tyndale prints his English translation of the New Testament of “The Bible”
“The Great Bible” published
First version of “The Book of Common Prayer” published
William Shakespeare writes his first plays
Robert Cawdrey publishes the first English dictionary, “A Table Alphabeticall”
Jamestown, the first permanent English settlement in the New World, established
The Authorized, or King James Version, of “The Bible” is published
Death of William Shakespeare
Publication of the first English-language newspaper, the “Courante” or “Weekly News”
First Folio of Shakespeare’s works is published
Publication of the first daily English-language newspaper, “The Daily Courant”, in London
Samuel Johnson publishes his “Dictionary of the English Language”
Britain wrests control of Canada from the French
Last native speaker of the Celtic Cornish language dies
George Washington defeats Cornwallis at Yorktown and Britain abandons its American colonies
British penal colony established in Australia
First publication of “The Times” newspaper in London
Noah Webster publishes “The American Spelling Book”
First English settlement at the Cape of Good Hope, South Africa
Lewis and Clark document exploration of routes to American West
Noah Webster publishes his “The American Dictionary of the English Language”
Abolition of slavery in the British Empire
British colony established in new Zealand
United States ends slavery after Civil War
British Broadcasting Corporation (BBC) founded
First edition of the “Oxford English Dictionary” is published
India and Pakistan gain independence from Britain
Sir Ernest Gowers’ “The Complete Plain Words” published
Second edition of the “Oxford English Dictionary” is published