The Memorial Peace Cross sits at the intersection of Baltimore Avenue, Bladensburg Road and Annapolis Road in Bladensburg, Md. (Mark Gail/FOR THE WASHINGTON POST)

What is striking about the Peace Cross case before the Supreme Court is what it reveals about our country’s religious transformation since the war memorial was erected in 1925.

In early 20th-century America, the prevailing view was that a Christian cross was the right and proper way to honor the war dead. From what we know about the men listed, it would appear that the 49 World War I soldiers commemorated by the monument in Bladensburg, Md., were Christians.

The monument was built with private funds, but by midcentury, the land was formally transferred to the government to maintain.

Yes, the First Amendment and state constitutions prohibit government establishment of religion. But for much of our early history, the United States was a semi-established Protestant country.

Up through the 1950s, when the local government took over maintaining the Peace Cross, American culture was dominated by Christian — generally Protestant — symbols and expression, including in public schools.

Protestant hegemony led to conflicts and division, especially after immigration of Roman Catholics and Jews surged in the late 19th century. Protestants supported separation of church and state, but only if the “separation” left them in charge of the culture.

Consider the “Bible wars” in the late 19th century over whose version of the Bible would be read in public schools. Protestants insisted that only their Bible was the “common faith” appropriate in American schools.

Or consider the textbooks of the time that instructed students using stories from the New Testament. When Jewish parents complained in New York, the committee appointed to investigate the matter appeared genuinely puzzled by the objection. After all, the textbooks were simply teaching what was widely held (by the majority) to be truth necessary for morality and citizenship.

When Protestants — across their own deep differences — agreed to “no establishment” they did not envision giving up cultural dominance. For many in the majority, “Christian” (by which they meant “Protestant”) was synonymous with “civilized.” As late as the 1950s, people in my part of the Deep South were still saying, “She or he is a good Christian,” without knowing whether the person was Christian or not.

Of course, Protestant hegemony could not and did not last. Immigration, secularization and other factors led to the breakdown of Protestant cultural dominance over the course of the 20th century. By midcentury, Protestant America was recast as “Protestant, Catholic, Jew,” as famously described in Will Herberg’s 1955 book.

Some vestiges of the old order were removed in the 1960s when the Supreme Court struck down state-sponsored prayer and devotional Bible reading. It is often overlooked that by the time the court finally ended those practices most public schools had already abandoned them in an increasingly diverse America.

The Peace Cross fight before the high court evokes another era, a time when many Americans would have seen it as natural and uncontroversial to commemorate the war dead with a cross. But would any local government today erect a Christian cross as a memorial to fallen soldiers or, as happened in this case, accept the transfer of a cross memorial to be maintained by tax dollars? It seems highly unlikely.

Today the United States is one of the most religiously diverse societies in the world, with growing numbers of people who have no religious affiliation. Arlington National Cemetery and all other cemeteries for veterans have a variety of religious and nonreligious symbols on grave markers. No one religious symbol could — or should — be used to represent all people.

More than lawyers and judges, it is our nation’s diversity of religion and belief that is finally pushing our country to live up to the promise of “no establishment” under the First Amendment. Our once Protestant-dominated culture is being transformed into a culture where diversity of religion and belief is increasingly visible and powerful.

Americans are discovering that when government stays out of religion, leaving religion free to be authentic in the marketplace of religion and belief, society can move closer to the level playing field promised by the First Amendment.

In his argument for the Constitution, James Madison wrote that the “multiplicity of sects” is the “best and only security for religious liberty in any society.” In other words, where there are many religions and beliefs, no one group can dominate or oppress the rest.

Madison was in this, as in other things, prematurely optimistic. As it turned out, the many Protestant sects of his time were eventually able to agree on a “common faith” that would dominate our schools and culture for generations. But today Madison’s insight rings true.

America’s extraordinary diversity of religion and belief makes it difficult, if not impossible, for any local government or school to get away with attempts to reassert the Protestant hegemony of our early history. The country is no longer the semi-established Protestant society, in numbers or in culture, that it was when the Peace Cross was erected in 1925.

A majority of the Supreme Court may find a way to keep the Peace Cross on government land by appealing to history and tradition. If so, the justices will have to once again — as they did with the creche in the holiday display cases — transform the cross into a secular symbol. Government appropriation of religion always ends badly for religion as well as for religious freedom.

However the court decides the case, the United States will never again be a country where the government can use the Christian cross as the universal symbol for memorializing our war dead, or for any other purpose. Our diversity of religion and belief is so great that any attempt to impose one symbol on everyone would be met with outrage and opposition in almost every American town or city.

Changing demographics, not Supreme Court justices, will ensure that America finally lives up to the full promise of “no establishment” of religion. Government neutrality among religions and between religion and nonreligion is a very difficult ideal to achieve.

But thanks to the voices raised by Americans of many faiths and beliefs, we are closer now than at any time in our history.

Charles Haynes is founder of the Religious Freedom Center at the Newseum in Washington.