Throughout this series I have been looking for answers for two questions: Why does whisk(e)y have two spellings? and Why does the US favor using whiskey while most of the world spells whisky without an e? The answer for the first question, as it turned out, is fairly simple and straightforward. Whisk(e)y entered the English language at a time when spelling was not standardized (i.e. before dictionaries) and it was common to have multiple spellings of one word. However, the answer for the second question is more complicated.
Throughout the history of the word, neither the US nor the UK have ever exclusively used one spelling of whisk(e)y. But, since the 1850's the UK has favored spelling whisky without an e. In the US, whiskey, with an e, has only been used slightly more often that its alternate. Mid-nineteenth century dictionaries and literature from the United States demonstrates that both spellings were used interchangeably without any geographic connotation. However, after 1960 whiskey became the preferred spelling in the US.
While I had looked at books, etymology and dictionaries I was missing one other influential written source: Newspapers. Using the California Digital Newspaper Collection, which includes papers statewide from the 1840's to the present, I found that there was no differentiation between the use of whiskey or whisky in papers from the mid-eighteenth to early twentieth centuries. For some unknown reason, the use of whisky skyrocketed from 1880-1890 though almost none of it referred to aged grain spirits made in Scotland.
I began to wonder what might have changed around the 1960's that could explain why the US started to prefer the spelling of whiskey over whisky and when the spelling's became embedded with geographic meaning. As I continued to look at newspapers I discovered something interesting. In 1950's the Associated Press, Los Angeles Times and the New York Times, all published style guides that, among other things, gave instructions on how to spell whisk(e)y. These style guides are important not only because these institutions have large readerships but also because other papers, magazines and writers use them as a reference when publishing their own works. The AP Stylebook spells whiskey with an e but allows an exception for whisky when referring to Scotch. Similarly, the LA Times Stylebook followed the AP guideline for whiskey but they expanded their exception to cover both Scotch and Canadian whisky. These style guides seem to be the first published sources in the US to link the spelling of whisk(e)y with a geographic location. The appearance of these style guides in the second half of the twentieth century mirrors the changing preference in the US for spelling whiskey with an e and the idea that whisky (for the most part) refers to non-US spirits. While it is certain that the AP and LA Times did not create these distinctions, the evidence suggests that they were the first to codify them.
The interesting outlier among these style guides was the New York Times. From 1950 to 1976 The New York Times Manual of Style required its writers to spell whisky without an e in all circumstances. However, in 1999, for some unknown reason, the Times made a 180 degree change and decided to spell whiskey with an e no matter where it was made. Everything seemed fine until late 2008 when an internet controversy erupted about the Times' insistence that Scotch whiskey be spelled with an e. In February 2009, after a flood of negative feed back from readers about their one size fits all policy, the Times changed their style guide again. They adopted the rule followed by the LA Times which spells all whiskey with an e except when referring to Scotch and Canadian whisky.
Since newspapers are one of the most prolific sources of written language in the country, it makes sense that the change in how whiskey and whisky were used would be reflected here first. But, just like dictionaries, style guides are reflecting and permeating language as it already exits, not creating new words or rules. That being said, these style guides provide the best answer for why the US began to favor the spelling of whiskey when in the 60's and why whisky referred to aged grain spirits made outside the country.