Answer:
An example of this is the Germanic language group.
Explanation:
The Germanic languages are part of the Indo-European languages. Initially, they formed as a separate language after the migration of the proto-Germanic people in Europe. The Germanic people though dispersed over a wide area over time, with natural barriers and other people groups between them, which led to isolation from each other.
The split basically came in the form of one group living in Scandinavia, one group in eastern Germany and along the coast of what is now Poland, and one group moved back to the east though not so far to reach the ancestral lands, so over time they developed different dialects. Scandinavia was relatively isolated because of the sea and for a long period the people didn't have much contact with the other Germanic people, but also they had a lack of influences from other languages, so in many ways, they persisted speaking a language very close to the initial proto-Germanic. The Germanic people of what is now Germany and Poland were isolated from the other Germanic people but were in constant touch with other people groups, which gradually led to divergence and formation of a separte language. The Germanic people that moved eastward, the Gothic groups, were very often in alliances with other people groups but also mixed with many people groups, so this led to the mixing of languages as well and the language they have developed, while still retaining the Germanic core, was much different.
