Under what conditions were language boundaries created?

There are no language boundaries. One of the interesting things about language is that it constantly changes and people add Words to their own language from other sources. English is not a pure language and much of it comes from other sources. Take the Word "beef" that is a a French Word added to English from the Norman invasion of England. For 300 years after 1046 the British kings didn't speak English, but French. Even today the Queens menus are in French.