Without fail the question about how to spell "whisky" comes up in tastings. A quick google search and you will find diagrams showing you this "rule": If the country name has no 'e', then the spelling of whisky is sans 'e' as well.
That rule is a garbage rule. It lacks an understanding of the history, stories, competition, and brilliance of whisky. Beyond that, it's just plan wrong. Otherwise, all whisky made in the United States would have an 'e' in the spelling. One of my personal favorite American brands is Maker's Mark...and, you guessed it, the spelling is "whisky" on every bottle.
American whisky also has federal and local laws concerning the production, distribution, and selling of whisky. The Alcohol and Tobacco Tax and Trade Bureau (TTB) does not have a labeling requirement for the spelling of whisky (the official designation is without the 'e', but allowances are made for use of the letter based on tradition). If you look, however, at a state like Colorado the term "whisky" never comes up in the statutes. Instead, Colorado favors the spelling with an 'e'.
Some folks will tell you that the spelling of whisky in the United States is then tied to the family heritage of the distiller. In Scotland whisky is always spelled without the 'e', while in Ireland the word is always "whiskey". Accordingly, in the United States, the commonly accepted spelling of whiskey with an 'e' is owed in some part to the influx of Irish immigrants during the late-1700s.
Great, so that is settled, right? Nope.
The first question you should ask then would be, "why do the Scots and Irish spell it differently?" The second question you should ask is, "are there any brands that do not adhere to this rule?".
Let's tackle the second question first. The easiest example to debunk the heritage-based spelling comes from George Dickel Tennessee whisky. George Adam Dickel, the founder and namesake, was a German-born American business man. He had no familial ties to Scotland. He simply preferred the shorter spelling. I always say it is because he was German and therefore preferred the efficiency of the shorter word.
This puts us to the real question of why the Scottish and Irish spell the word differently. I have heard people say it comes from the variances in Irish Gaelic and Scottish Gaelic. However, the Irish word for whisky is "uisce beatha" and the Scottish word is "uisge beatha". This does not really clear anything up. If anything, the anglicized words should be whisky and whisgy (or perhaps, whiskey and whisgey)
Side note: if you really want to impress people, let them know the Irish Gaelic word for whiskey with an 'e' is actually fuisce, which is synonymous with uisce beatha.
Bottom Line: The spelling is not backed in historical fact. Instead, it is backed in historical lore. The entire point of talking about whisky is to tell stories. It ties our imagination to the drink and livens our senses. Here is the story I like to tell for why the 'e' sometimes appears:
The Irish invented the modern form of whisky. They did not invent distillation nor whisky...just it's modern form. The Scots got a taste of it and went to Ireland to figure out what the Irish were up to. Most of them took up employ at the Irish distilleries, some even founded Irish brands (Jameson). Others, however, went back to Scotland and worked on perfecting the process. This, in turn, made the Scottish version of whisky superior. The Irish were incensed and felt it was their duty to reclaim the throne as having the "best" whisky. The Irish began triple distillation to smooth out the harsher notes and added the letter 'e' to distinguish this newer, better, product from that of the Scots. The name change took and it has created the worlds most ridiculous argument ever since.
Author's Note: Clearly I prefer the spelling without the 'e'. In writing, spell it consistently throughout, unless you are talking about a specific brand. Then pay homage to the brand by spelling it the way they spell it.