Retailing historians who care about these things — if indeed any exist — will remember the four weeks that ended in mid-July 2012 as the month when Walgreens changed mass retailing.

Retailing historians who care about these things — if indeed any exist — will remember the four weeks that ended in mid-July 2012 as the month when Walgreens changed mass retailing.

Rarely in the annals of mass retailing — and never in the history of the chain drug industry — has any one retailer made so profound an impression on the industry in so short a time.

Looking at the events in reverse chronological order, the drug chain most recently settled its dispute with Express Scripts, ending an impasse that began at the beginning of January and an acrimonious and contentious relationship that had existed long before that date. While neither party is anxious to discuss the details of the settlement or the reasons the parties finally came together, this was a major victory for Walgreens, if only in the sense that it put the issue behind it.

Over the short term, since Walgreens and Express Scripts parted ways at the start of the year, the drug chain unquestionably suffered, losing sales and customers at rates that alarmed the retailer’s friends and confused and comforted its competitors. In June alone, Walgreens’ sales declined 6.8%, while same-store sales dropped 10%. In terms of customer counts, the decline was precipitous. And the biggest beneficiary was the drug chain’s biggest competitor.

But for the long run, the fact that the agreement was reached consistent with Walgreens’ principles is good news for community pharmacy.

Before the Express Scripts issue was settled, Walgreens made news of another kind, buying the 144-store USA Drug retailer. While not as significant as the book-end deals that surrounded it, the purchase further solidified the drug chain’s already strong position in the middle of the country. Additionally, it created speculation as to just what Walgreens will do with a group of stores that are considerably smaller than its present format.

Speaking of speculation, no transaction in recent memory has aroused so much guessing as has Walgreens intentions in announcing a merger with Alliance Boots, the global drug retailer/wholesaler that dominates in Europe and is a significant presence in most other parts of the globe, North America excepted.

Would-be analysts have Walgreens opening drug stores in Europe, despite the fact that the Boots model is every bit as impressive as the Walgreens brand, and Boots, already the dominant drug chain in the United Kingdom, is a presence in several other European locations as well.

So we can safely dismiss the idea of Walgreens rushing to open drug stores outside the United States. No, the retail attraction for Walgreens, according to those who really know, is the expertise Alliance Boots brings to the Deerfield, Ill., drug chain, most specifically in the areas of drug wholesaling, generic drugs and Boots brand products.

To cite just one example, Boots house brands already record over $100 million in sales in the United States, through such retailers as Target, Sephora and Walgreens’ own online unit, drugstore.com. That may be a small number — but it has been achieved through a relatively small group of stores. Walgreens could doubtless increase that business many times over, both by adding retail outlets — its own — and by increasing the number of Boots brands available through Walgreens drug stores.

Then there’s the fact that Alliance Boots owns a line of generic drugs that is the equal, in many ways, of the generic assortments Walgreens now purchases from other sources. That reality opens up a list of opportunities most analysts have not yet even ­considered.

There’s more — much more. Most obvious is the fact that Alliance Boots boasts some of the brightest retail and wholesale minds that exist anywhere. Adding that talent to a Walgreens management team that is already acknowledged as one of the strongest in the industry gives the new entity an unparalleled advantage.

So, whatever your retail persuasion, you just have to take your hat off to Walgreens — and to Greg Wasson, the retailer’s marvelously exciting chief executive, who has already made observers forget that Walgreens was until recently a drug chain that excelled primarily in the monotonous execution of the same tired formula.