The word oestrogen comes from the Latin word oestrus, and oesophagus is a Latin word as well.
The oe spelling in Latin originally represented a diphthong [oj] ("oy"), but then later (in Latin) became a long vowel [ee]. When we borrowed such words into English, it was pronounced more like [i], [e], or [ɛ] (depending on the word), following English pronunciation rules.
And since we pronounce them like "estrogen" and "esophagus", the US English spelling was changed to reflect the English pronunciation more closely, by dropping the o. In British English, the connection to the original Latin spelling was retained.
(Something similar to this happened with, e.g., encyclopaedia (British) / encyclopedia (US).)
As mentioned in a previous answer to one of your questions, this is called Mid-Atlantic English and was commonly used in American films of the 1930s and 40s.
Wikipedia gives the following reasons that someone would use the accent:
- Intentionally practiced for stage or other use (as with many Hollywood actors of the past). A version of this accent, codified by voice coach Edith Skinner, is widely taught in acting schools as American Theater Standard.
- Developed naturally by spending extended time in various Anglophone communities outside one's native environment, most typically in North America and the United Kingdom.
- Learned at a boarding school in America prior to the 1960s (after which it fell out of vogue).
So essentially, this type of speech was never common and was only natural in the case of ex-pats.
Some examples of 'Mid-Atlantic' speakers:
Katherine Hepburn
Criticised for her shrill voice, she left Baltimore and studied with an acclaimed voice coach in New York City (Frances Robinson-Duff).
Cary Grant
After moving to the United States, he managed to lose his accent, developing a clipped mid-Atlantic speaking style uniquely his own.
Claude Rains
He grew up, according to his daughter, with "a very serious cockney accent and a speech impediment". He had elocution lessons in Britain and then moved to America where he played British, American and European characters.
Best Answer
The change in the vowel phoneme used in "God" certainly occured in American, not British, accents. One piece of evidence indicating this is that in a usual American English accent, the vowel of "God" has merged with the vowel of "father," while this is not so for a usual British English accent. The spelling provides a clue that the distinction in British English is due to retention of an original distinction rather than due to an innovative split.
Wikipedia, which is not such a reliable source but which is the best I have right now, says the change happened "from the 18th century on."
The general development of the "short o" sound goes like this:
Specifically:
In a usual accent from the south of England, the vowel in "God" currently tends to be somewhere around [ɔ], although often transcribed /ɒ/ due to tradition. It contrasts with both [ɑː], in "father," and [oː], in "laud."
In a usual Scottish English accent (not the same thing as Scots or Scottish Gaelic), the vowel in "God" is traditionally transcribed as /ɔ/, and it is merged with the vowel of "laud" but not with the /ɑ/ of "father."
In a usual "general" American English accent, the vowel in "God" is [ɑ], merged with the "father" vowel; in American English affected by the "Northern Cities Vowel Shift" it has been fronted to more or less [a]. In accents with the caught-cot merger "laud" has this same vowel; in accents without the merger "laud" has a distinct vowel usually transcribed /ɔ/, but often phonetically closer to something like [ɒ].
American English is not really so much more conservative than British English. Other innnovative phonological/phonetic elements that are more common in North American English than in British English are:
These are not universally present in American English accents, and yod-dropping and t-lenition exist in some British English accents as well, but these innovations are certainly more common in North American English than in British English.