"Keep calm and carry on."

That now famous phrase on ubiquitously reproduced posters was meant to maintain Brits' stiff upper lip amid an existential crisis. Commissioned originally in 1939 by Britain's Ministry of Information, the poster reflected a cohesive country under siege, with government and citizens alike rallying to a common cause.

Across the pond, America had its own totems of national unity, from Frank Capra's "Why We Fight" films to "victory gardens" to scrap-metal drives and beyond.

Eighty years later, another existential crisis, COVID-19, called for a similar approach.

And for a time, at least here at home, there were signs — literally, in the case of handmade placards in windows, on lawns or scrawled in sidewalk chalk, encouraging everyone that we're all in this together — that society would coalesce as the Greatest Generation had during the Depression and World War II.

But it didn't endure.

Instead, as the Pew Research Center commented in its report on a year of public opinion on the pandemic, as the crisis continued, "there was less and less common ground. Indeed, the biggest takeaway about U.S. public opinion in the first year of the coronavirus outbreak may be the extent to which the decidedly nonpartisan virus met with an increasingly partisan response."

This split, Pew stated, "stood out even by international standards: No country was as politically divided over its government's handling of the outbreak as the U.S. was in a 14-nation survey last summer."

The divergence between World War II unity and today's pandemic division is multifactorial. But it starts at the top, two historians said in reflecting on the one-year mark since March 2020's lockdowns began.

"The most striking difference is the response of leadership," said William P. Jones, a professor of history at the University of Minnesota. "Unity wasn't automatic or organic, but the way President [Franklin] Roosevelt responded was strikingly different from the way in which [former] President [Donald] Trump responded. He not only insisted that fascism represented a threat to the United States, but that the U.S. had a special role to play in defending democracy.

"And really important to the effectiveness of that call was the idea of shared sacrifice; the idea that all Americans would have to sacrifice for the broader public good, and also the sort of promise that this experience would actually improve America, and improve American democracy."

FDR's administration "went out of their way to really build that consensus," said William T. Johnsen, a now retired professor of military history and strategy at the U.S. Army War College.

The context of consensus-building in part reflected a more "rules-based society," Johnsen said. And it was one that "had come through the Depression, and everybody sacrificed through the Depression; it didn't matter whether you were a farmer in the Dust Bowl or a banker in New York that walked off the ledge. Everyone was pretty well hard hit."

That wasn't the case early on in the pandemic, when Wuhan, Italy and Britain were pretty well hard hit before New York became ground zero in America's COVID calamity.

So even though the virus eventually infected every corner of the country, the sense of shared sacrifice wasn't sacrament as it was in World War II and other previous crises.

Add to that disparate (even desperate) efforts from 50 individual states instead of an indivisible nation — in which the commander-in-chief tweets "LIBERATE MINNESOTA!", "LIBERATE MICHIGAN!" and "LIBERATE VIRGINIA!" (all states with Democratic governors) — and cohesion can turn into contention.

"The politics of the moment and the politicization of the disease is mind-boggling to me," said Johnsen.

This politicization was amplified at times by a media environment dramatically different from the war era. In the technological transformations, to be sure. But in the partisanship, too.

"Popular opinion was still shaped by the elites of the time, largely in the Northeast," Johnsen said. "You saw elites come together, [along with] newspaper and radio, and you can't underestimate fireside chats" from FDR.

Firing up partisans seemed to replace fireside chats and elite consensus during the pandemic, a fact reflected in research from the Center of Media Engagement at the University of Texas.

In an analysis of how different networks covered COVID, "Fox News and MSNBC were more likely to mention political figures and organizations than health officials and entities, signaling the politicization of coverage," Natalie Jomini Stroud, the center's director, said in an e-mail exchange.

"Essentially, we're seeing a pattern with COVID-19 that we've seen many times before. In a fragmented media environment where different outlets offer different messages about what is happening, audiences begin to develop different impressions, attitudes and behaviors," Stroud said.

"The ability to rally the public behind a particular issue depends critically on how politically polarized the issue is," Stroud concluded. "When responses and attitudes fragment along partisan lines, it is difficult to see how the public can be rallied."

To be sure, rallying could be derailing during World War II, both Jones and Johnsen said, such as in the infamous example of Japanese internment camps, as well as other marginalization of minority groups.

But in balance America more came together than came apart.

It was an era, Johnsen said, in which "everybody has a stake, there is a very foreseeable, easy-to-see threat, and the administration and the media are going out of their way to promote this idea that we are in this together."

Those dynamics could have described this era, too. But a nation riven with divisions didn't overcome them despite a deadly crisis.

And yet, although the signs may have weathered since those dark days that began last March, most weathering this crisis still sense that we truly are in this together, even if some government and media leaders belie that truth.

Seems that World War II-era Brits believed it, too. Because those wartime posters seen everywhere today were never actually hung.

Turns out, they weren't needed, as a unified society was already keeping calm and carrying on.

John Rash is a Star Tribune editorial writer and columnist. The Rash Report can be heard at 8:10 a.m. Fridays on WCCO Radio, 830-AM. On Twitter: @rashreport.