Guidelines:
Historical linguistics
The history of English
Language families
The comparative method
Analogy and borrowing
The causes of language change
Where the info can be found:
1 Our lecture or
2 Goerge Yule: The study of language,CUP, chapter 19 Language History and Change
or Victoria Fromkin, Robert Rodman: An Introduction to Language, Holt, Rinehart and Winston, Inc., USA, chapter 8 Language Change: The Syllables of Time