1. Chronology. The history of English can be divided into four periods:
1) The Germanic Period, the period from prehistory to the middle of the 5th century AD, when all Germanic tribes lived on the European mainland. Main events: mixing of Proto-Germanic with the languages of North European aborigines, breakup of Common Germanic into northern and western dialects, borrowing of many Latin words into West Germanic (the First Latinate Borrowing).
This period ended in 437 AD when three closely related West Germanic tribes, the Angles, Saxons and Jutes, began migrating from the European mainland to the British Isles. This migration set the Anglo-Saxon off on a separate course from continental Germanic dialects.
2) The Old English, or Anglo-Saxon, Period, the period from the 5th century, when the main migration into Britain was accomplished, to 1066, the year of the Battle of Hastings, when the Anglo-Saxon rulers of England fell to Norman French invaders under William the Conqueror. Main events: second period of Latinate borrowing which accompanied the conversion to Christianity in 597 AD , mixing of Anglo-Saxon with the language of the Viking invaders (Old Norse) causes significant losses of grammatical endings, first known works of English literature appear (Beowulf).
3) Middle English, the period beginning after the 1066 Norman invasion which saw the gradual merger of two languages--the Germanic Anglo-Saxon and the Latin-based Norman French--into one language. This was accomplished roughly by 1450. The most extensive changes in English vocabulary occured during this period. Henceforward more than half the English vocabulary is of Latin (or French) origin and only a minority is of Germanic origin.
4) The fourth and final period, from about 1450 to the present, could be called the period of Modern English. Early Modern English is said to have lasted from about 1450-1600. This early phase witnessed a change in the pronunciation of most of the vowels, called the Great Vowel Shift. Also, English replaces Latin as the language of learning, and many new words coined from classical Latin and Greek roots. After 1600, English did not undergo any major changes in phonology or grammar. The second phase of Modern English, Late Modern English, witnessed the spread of English around the globe, the development of overseas colonial dialects, and massive increases in vocabulary under the influence of technological and scientific achievement. Today, English is arguably the most important system of communication on earth, the closest thing we have to a worldwide lingua franca.
2. Language mixing
Although modern English is classified as a Germanic language because its grammar and basic vocabulary are Germanic, English today contains words borrowed from hundreds of different languages. Many of these words we don't even think of as borrowed: mosquito (Portuguese or Spanish); coach (Hungarian); pajamas (Hindi); bungalo (Bengali); tulip, turban (Turkish); taboo (Tahitian); okay (Chocktaw); typhoon (Chinese); So long (Malay).
Let's review the main sources for words borrowed into English.
1) North European aboriginal terms borrowed into Common Germanic (before 1500BC)
2) Latin terms borrowed into West Germanic (100BC-400AD)
3) Christianized Latin terms borrowed from Frankish into Anglo Saxon (after 587AD)
4) Old Norse mixed with Anglo Saxon (700-900AD)
5) Norman French mixed with Old English (1066-1300AD)
6) Classical Latin and Greek roots used to coin large numbers of new words (1500- to present)
The mixing of several related IE dialects has produced a rich collection of synonyms in modern English. The resulting lexical doublets tell a lot about the history of the language:
forgive/pardon Latin influenced calque from 6th cent. vs. Norman French borrowing
shirt/skirt Native Anglo Saxon word vs. Old Norse borrowing
cow/beef Native Anglo Saxon vs. Norman French borrowing
dish/disk Older (6th cent.) Latin borrowing vs. post-Medieval Latinate coinage
chief/chef Older Norman French borrowing vs. recent borrowing from French