Perhaps, at the very beginning of history the mankind spoke one language. But later time this language changed. Because of what it occurred? Reasons a little. People in search of food looked for new areas of dwelling. Arriving to new places and growing roots, they spoke language of ancestors, a pronunciation over time, the name of subjects changed, old and unnecessary words went out of use on a new place. New vital conditions demanded new words for their description. And if people moved in already populated places, two languages merged, both changed.
Approximately thus appeared from Latin - English, Norwegian, Swedish, Danish.