Lets consider this in two parts: Mead as a beverage and western drinking habits.

In Proof: The Science of Booze, Adam Rogers states that one of the two earliest and most probable examples comes from Jiahu, China and is a mixture of rice, hawthorne fruit, wild grapes, and honey. The rigid idea of which drinks are which (mead, beer, wine) isn't really formalized for a very long time. Humans drink what is available and fermentable and often that involves mixtures of a variety of different bases, as long as they provide the necessary sugar. As humans got better at creating consistently alcoholic products, they were able to bring in other sources, such as grains, which require more work to produce alcohol. Grains are also much easier to domesticate and work with than bees, though humans were trying very hard to do that too. Since honey was comparatively more difficult to attain, it didn't take long to be edged out by more domesticated sources such as barley for beers and grapes for wine. Keep in mind, this is all dated to about the time humans are creating their first permanent settlements and learning about the domestication of crops, so as humans spread across the globe, they were taking this knowledge with them.

Next, lets consider those that we generally think of as the 'fathers' of mead: The Vikings (Collection of Norther European Tribes). For this section, my source is Make Mead Like a Viking, by Jerome Zimmerman*. Again we see honey combined with a variety of other fruits, grains, and spices in order to make a drink referred to as 'grog'. Based on evidence found at grave sites, there was a ritualistic element to the use of mead, as well as a class element. Only the rich (royalty) could even afford to use honey. While they may have taken pride in it, it is difficult to develop a wide-spread regular use of something that is reserved for the wealthy. This is also true of Wales and Ireland. Now, in my mind, when you say "The West", you are referring to America, England, France, and the surrounding areas. While the Northern European Tribes certainly had their victories, I am of the opinion that contemporary 'Western' culture is influenced a great deal more by the Roman empire and the subsequent English, French, and Italian societies. None of these were societies that particularly valued mead and its associated beverages.

For most of human history, alcohol production was a cottage-industry, specifically it was a woman's job to make alcohol at home for her family. Zimmerman credits the commercialization of alcohol production in the 18th and 19th century with the steep decline in the production of mead, since grains were significantly easier and cheaper to use on a larger scale. Between the development of the Coffey still in 1830 and the large scale production of significantly more palatable spirits, the industrial revolutions drive to remove home production of a wide variety of products, and western societies ongoing obsession with all things French, it's not hard to see why Zimmerman pinpoints this time as the 'death' of mead.

In my opinion, at the tail end of the first cocktail revolution Mead very well could have been about to make a come-back. Spirits were certainly in fair use, but fortified wines and champagnes were making their way into the average American's glass. Given a little time, mead might have done so as well as American bartenders searched for new and exciting things to create drinks from. Unfortunately, prohibition began in 1920, effectively putting a halt to the cocktail revolution and American experimentation. While some spirits were able to whether the storm under the guise of medicinal and some wines carried forth due to their religious applications for Catholic and Jewish parishioners, the vast majority of alcoholic beverages fell victim to the Great Experiment. If the industrial revolution killed mead, prohibition is the one that hid the body.

As far as I can tell from my reading, nothing 'happened' to mead. It never faced an outright assault the way absinthe or whiskey did. There was no war against mead, because it was never important enough to begin with. It was far too expensive to make on an industrial scale and by the time people cared to make alcohol at home anymore, it was too much of a pain. The only people who might have been making it were the beekeepers themselves, but they would have been able to sell their honey and beeswax for a great deal more than their mead so if the beekeepers were making it, it was for themselves only.

*Zimmerman has a bit of a poetic, fanciful style of writing which always makes me somewhat leery of using him as a source. You might be better off going directly to his source, Patrick McGovern's Uncorking the Past. Unfortunately, I haven't read this book yet. I have only the references to it from other authors.

How the hell did the ancients figure out that fermenting honey and water would lead to alcohol??

Mead was never as widely popular as beer or even wine was. Mead was most popular in Scandinavia, Poland and Wales during the middle ages but even in those places mead was considered a luxury drink and beyond how much it was enjoyed at an aesthetic level it's consumption was an act of social signaling that illustrated someone was part of the upper class and a person of means. Wine was the other beverage that was an effective social signal for wealth in Western Europe and eventually it surpassed mead even in mead's strongholds. Partially this is because Wine was the drink of the Romans and even long passed the crumbling of the Western Roman Empire, Roman culture was seen as the apex of human achievement and anything associated with it made it an effective social signal. Another aspect that isnt well understood about wine at a historical level is that the grape variety (vitis vinifera) used to make wine has a very unique property: beverages made from it maintain sweet tasting fruity properties even after all sugar has been fermented out of it. Its also naturally high in acid and humans have a weakness for fruity and tart flavor combinations. Mead by contrast has a harsher and less complex flavor profile which would be less appealing to most people.

So the short of it, is in places where mead was popular as a luxury item, it eventually lost out to wine due to social and aesthetic dynamics.