Before that we had the Romans but only about 200 Latin loanwords are inherited from that time. The Celts were the earliest of course, but very few words have lived on. Many of our place names, however, have Celtic origins.
By 597AD the Christian missionaries, led by St Augustine, moved throughout the country. The language of the Church is Latin and many new Latin words were injected into the vocabulary.
The Vikings arrived in 789AD and they brought another 2000 words as well as place names such as Whitby and Grimsby. King Alfred used the English language to develop a sense of identity amongst the people.
The Normans then arrived in 1066 bringing French with them, this was used for over 300 years as the language spoken by the most powerful people. Latin was still the language of the Church but most of the population used English in their everyday lives. Thousands of French words became entrenched in our vocabulary.
During the 100 Years War French was regarded as the language of the enemy and the status of English rose.
Since the Industrial revolution our vocabulary has been hugely expanded by the inclusion of technical and slang words from over 200 years of wonderful discoveries and innovations in the fields of art, theatre and science bringing words from across the globe.