Phonological history of English vowels
In the history of English phonology, there have been many diachronic sound changes affecting vowels, especially involving phonemic splits and mergers. == Great Vowel Shift and trisyllabic laxing == The Great Vowel Shift was a series of chain shifts that affected historical long vowels but left short vowels largely alone.
Source: Wikipedia — Phonological history of English vowels (CC BY-SA 4.0)