Not that it’s any consolation to booksellers, publishers or authors — or for that matter, readers — but Amazon‘s dramatic price slashing this past weekend, called “an open declaration of war against the industry” by at least one bookseller, may in fact have been a declaration of war against a specific competitor: Overstock.com, which had announced a “10% Off Amazon’s Book Prices” deal on its homepage.

As we noted in our weekend report, Amazon’s stunning discounts were first flagged by leading industry trade newsletter Shelf Awareness, which reported in a special Saturday morning alert that price reductions of “between 50% and 65%, levels we’ve never seen in the history of Amazon or in the bricks-and-mortar price wars of the past.” A wide array of bestsellers were having their prices slashed, including “Inferno by Dan Brown, which has a list price of $29.95 but is available on Amazon for $11.65, a 61% discount; And the Mountains Echoed by Khaled Hosseini, listed for $28.95, offered at $12.04, a 58% discount; Lean In by Sheryl Sandberg, listed at $24.95, available for $9.09, a 64% discount …”

But a report by Zak Stambar for internetRetailer details what Amazon may have been reacting to: Overstock’s Thursday announcement that it would beat Amazon’s prices by 10% in a promotion applying not just to bestsellers but to “the roughly 360,000 titles sold on both Overstock.com and Amazon.com.” An Overstock spokesman explained, “Everyone is accustomed to looking at Amazon when they’re shopping for books,” he says. “We’re hoping this will get them to look at Overstock first.”

Whether it got consumers to look or not, it does seem it got Amazon to take a look, which in turn elicited Amazon’s typical, scorched-earth response to simple competition (remember the two-pence price war with Sony?).

Overstock’s website calls the promotion a “one-week only” event, although Stambar reports that “Overstock says it will examine consumers’ response to the promotion before it sets an end date.” But however long it takes to play out, you can bet the farm that pitbull Amazon’s jaws will remain locked on poodle Overstock’s throat till it succumbs.

Meanwhile the industry will perversely and half-heartedly root for it to continue until Amazon puts itself out of business, just as the British industry did during the Sony price war. But of course, Amazon has never had to respond to economic gravity before, so why should it now? The longer Overstock holds out, the more Amazon’s stock value will no doubt rise.

And in the end, even if the price slashing was not a message to the industry, that industry’s alarm is no less justified. In the wake of the government’s successful lawsuit against five major publishers and Apple for supposed price-fixing, and President Obama’s shocking decision to visit an Amazon warehouse to make a policy speech about jobs, Amazon’s flagrant flaunting of antitrust laws against loss-leader pricing seems bolder than ever … and its devaluation of the book, in more ways than one, continues in a race to the bottom.