While you're waiting for other answers here, you might find this section of our FAQs to be interesting, as well as the section a bit lower down on the same page on the Transatlantic Accent.

The Great Vowel Shift was still going on in the early days when America was being settled. Prior to that, English vowels were pronounced the same way as vowels in French, Spanish, Italian, etc. Continental English was far more affected than American English - though obviously neither of us pronounce our vowels the way Romance languages do. There was an ELI5 on the subject from a month ago, and with the top commenter being an English prof from Alabama. Quick disclaimer: the video he linked provides good basic information on where Old English and Modern English come from, and how to think of how languages develop, but doesn't actually address the specific topic.