WELLS, Maine — With almost no attention, and surely no grand commemoration, Maine this summer marked an important American anniversary that, despite its unheralded nature, provided one of the more vital, and less well-known, turning points in the nation’s history.

It was 200 years ago this summer that, by a margin of 9,959 votes, residents of this windswept state agreed to end its status as a far-flung province of Massachusetts and seek statehood of its own. That vote set in motion a struggle in Washington that brought the issue of slavery to its most prominent point yet in the four-decade-old life of the young republic.

On Capitol Hill, lawmakers paired the petition of Maine, which would ban slavery, with the petition of Missouri, which would permit slavery, resulting in what became known as the Missouri Compromise. Thus Maine’s vote on July 26, 1819, can be considered a landmark turning point.

The double mass murders several weekends ago prompted questions over whether they might provoke a turning point in the nation’s long debate about gun control. Already one Republican lawmaker, Rep. Mike Turner of Ohio, who had an “A” rating from the National Rifle Association, announced he had had a change of heart, explaining that the shootings in his congressional district were a “catalyst for a broader national conversation about what we can do to stop these mass shootings.”

There have been several important turning points in American history, many of them, like the Maine referendum, traceable to a specific date. Here is a (necessarily incomplete) list of some of them, omitting the obvious ones of Dec. 7, 1941, and Sept. 11, 2001:

Aug. 20, 1619. The arrival of the first slaves in what would become the United States would shape American history from its Colonial days through contemporary times, providing the country with its “original sin” and its most persistent challenge.

Sept. 17, 1787. The signing of the Constitution, the founding document of the country, established the great American political experiment.

Nov. 6, 1860. The election of Abraham Lincoln to the presidency is without question one of the hinge events in our history. The first avowed, unapologetic anti-slavery president, his ascension to the White House set in motion the Civil War that had been looming for decades. “This,” Gettysburg College Civil War historian Allen Guelzo said in an interview the other day, “is where the door is firmly slammed on slave-owning presidents or dough-faces who would do the bidding of the slave South.” Within a half-decade, slavery would be abolished.

July 9, 1868. The passage of the 14th Amendment provided for “equal protection” under the law and established rules for citizenship that granted full rights to all Americans. In a new book on the Reconstruction amendments to be published next month, the distinguished historian Eric Foner argues that the measures constitute a “Second Founding” for the United States and contends that the 14th Amendment is “a powerful force for assimilation of the children of immigrants, and a repudiation of a long history of racism.”

Feb. 15, 1898. The causes of the explosion of the USS Maine have been a controversy for a century, but there is no controversy about its effect. It drew the United States into a war that would provide it with its first colonies, make imperialism one of the themes of American history, and bring the country into world affairs in a new way.

Aug. 18, 1920. The expansion of the franchise to women laid the groundwork for important advances for half the population that still have not been fully realized.

Nov. 8, 1932. The election of Franklin Delano Roosevelt amid the Great Depression ended a dozen years of Republican rule, gave form to a new electoral coalition that would be one of the principal characteristics of American politics for nearly a half-century, prompted massive federal intervention in the economy, and established a new paradigm for the role and conduct of an American president.

Aug. 14, 1935. The Social Security Act would change the way Americans retired and would inject Washington into the financial planning of every family.

Aug. 6, 1945. Last week marked the 74th anniversary of the atomic bombing of Hiroshima, inaugurating a frightful era of nuclear weaponry and establishing the United States as a superpower, a status it has held for three-quarters of a century.

Dec. 1, 1955. Rosa Parks’ refusal to move to the back of a public bus prompted the beginning of the Montgomery Bus Boycott, which, among other incidents, set the stage for the modern civil rights movement and the passage of the 1960s Civil Rights and Voting Rights Laws.

Feb. 9, 1964. The appearance of the British rock group The Beatles before 70 million viewers of the Ed Sullivan television show was the beginning of the post-Elvis rock era, the impetus for a dramatic change in men’s hairstyles, and, in time, one of the roots of a counterculture that included youth rebellion, wide drug use and mass protests of American Vietnam policy.

June 28, 1969. A police raid at Greenwich Village’s Stonewall Inn 50 years ago this summer began the modern gay rights movement that transformed American views of police brutality, sexuality and marriage.

June 17, 1972. The Watergate break-in triggered a great White House scandal, the first resignation of a president and new campaign-finance laws.

Nov. 4, 1980. The election of Ronald Reagan, a onetime FDR supporter, signaled the demise of the New Deal coalition, began the age of tax cuts, and ended the Roosevelt-era notion that government was the answer to the nation’s economic, social and cultural ills.

June 29, 2007. The introduction of the iPhone transformed global culture and assured that more people would read this essay on their phones than in print.

Nov. 8, 2016. Already it is clear that the election of Donald J. Trump was a major turning point in U.S. history, an indication that the disruption that had caused upheaval in the economy and culture of the country had come to the politics of the nation, endangering decades-old nostrums about trade, national security and presidential comportment.

Aug. 3-4, 2019. Though tragic episodes in Colorado, Nevada, South Carolina, Pennsylvania and Florida numbed the nation to mass murders, the twin shootings last weekend have the potential of being a turning point.

Caveat: The British historian A.J.P. Taylor wrote that in 1848 “Germany had reached its turning point and failed to turn.” Before the year is out, we may know whether the same might be said here.

David M. Shribman is a former and now emeritus executive editor of the Post-Gazette and a nationally syndicated columnist.