Final answer:
The French had the largest impact on the evolution of Middle English, particularly after the Norman Conquest in 1066, which led to significant French influence on the English vocabulary.
Step-by-step explanation:
The group that had the largest impact on the evolution of Middle English was the French. During the Middle Ages, following the Norman Conquest in 1066, Norman French became the language of the ruling classes in England. This had a profound impact on the English language, which at that time was influenced primarily by Old English, a Germanic language. The integration of French words into English vocabulary contributed to the transformation into what we now recognize as Middle English. While there were other influences on the English language, such as Latin through the Church and some borrowings from other languages due to trade and war, it was the French language that was the most influential during this formative period.