When I investigate societal breaks, I investigate morals, ethics, and presumptions. I also investigate cultural varieties and similarities through behavioral and customary tendencies. With that all being said, I am aware of a break in traditional (what was once known as normal) academic thinking at the break of the 20th century. This thinking spilled over into political discourse. Of course, this whole phenomena started well before that. I wrote about it in an article recently where I mentioned that there was a hairline fracture that split the thinking of American traditionalists and progressive intellectuals.
In the 19th going into the 20th century, the Unitarian Church (a secular "church") was the catalyst. Traditionalists (such as the clergy and church) began to slowly halt providing leadership in our public schools and university’s (prior to this was a purely homeschooling education). Harvard was taken over by the Unitarian church, and as the quality of public education began to decline, Horace Mann (the "father of progressive education") would convince the state of Massachusetts that the best way for education to grow would be to have the government take control, instead of the private sector (like families and churches).
As traditional American doctrine was neglected, the competing ideology of socialism has taken off. Karl Marx’s book, which was written in 1844, never had much influence in American society. That was until we had backslid from Christian principles of economics and dabbled in greed. Thus, monopolies would form and grow. Wealth was accumulated, instead of employing the extra wealth to meet the needs of the poor and society itself. Self-culture (or individual interest) began to replace the common good of the community. What followed was indoctrination into “self-culture,” a human thought process of “me, myself, and I” which closely follows materialism. To break open a political divide for control and power, there must be a catalyst to enable this cultural shift. Thus, secular humanism was born.
Marshall Foster writes that “in the loft restaurant above Peck’s restaurant at 140 Fulton Street in lower Manhattan, a group of young men met to plan the overthrow of the predominately Christian world-view that still pervaded America. At this first meeting five men were present: Upton Sinclair, 27, a writer and a socialist; Jack London, writer; Thomas Wentworth Higginson, a Unitarian minister; J.G. Phelps Stokes, husband of a socialist leader; and Clarence Darrow, a lawyer.
Their organization was called the Intercollegiate Socialist Society. Their purpose was to ‘promote an intelligent interest in socialism among college men and women.’ These men were ready to become the exponents of an idea passed on to them by an obscure writer named Karl Marx—a man who never tried to be self-supporting but was supported by a wealthy industrialist who, inexplicably, believed in his theory of ‘the dictatorship of the proletariat.’ Although a small group in the beginning, these adherents of socialism more than succeeded in their task.”
“By using the proven method of gradualism, taken from the Roman general, Quintus Fabius Maximus, these men and others who joined with them slowly infiltrated” the public schools of our nation. By 1912 there were chapters in 44 colleges. By 1917 there were 61 chapters of student study groups of the League of Industrial Democracy. “At that time John Dewey, the godfather of progressive education, was the vice-president of the league. By 1941 Dewey had become president and Reinhold Niebuhr, the liberal socialist theologian, was the treasurer.” 
The beginning of the end of traditional America had become entrenched. Dr. Stephen K. McDowell mentions that “the loss Christian tradition, character, and responsibility led to the failure of many banks in the early 1900’s. To remedy this situation, power was granted to a centralized Federal Reserve Board in 1913. But this unbiblical economic structure and lack of character produced many more problems. Within 20 years, the Stock Market had crashed, and America was in the midst of the Great Depression.”  With the propagation of socialism, people were ready for Roosevelt's “New Deal,” such as Social Security and other welfare agencies, which ultimately set up the State as provider rather than God.
It was exactly this break in thinking that brought back certain negative concepts of “race.” This time however contemporary and glorified in other ways geared towards bending one’s political thought or will towards the leftist ideology, saturating into any historical topic. Our history, as of the 1900's, has been manipulated to make certain academic agenda's fit the needs to a political end as mentioned before. A great example is the evidence in our academic texts over the course of this time.
Professor Paul C. Vitz in a government funded study he conducted in the 1980s on whether bias exists in public school textbooks. His study clearly showed bias and censorship exists, and the nature of the bias is clear: “Religion, traditional family values, and conservative political and economic positions have been reliably excluded from children’s textbooks.” 
Vitz wrote that while the bias may not be deliberate, a “secular and liberal mindset appears to be responsible.” And he points out that the bias is primarily manifested by exclusion. As an example, “sixty representative social studies textbooks were carefully evaluated” and “none of the books covering grades 1 through 4 contain one word referring to any religious activity in contemporary American life.” While these social studies texts mention the family, “the idea that marriage is the origin and foundation of the family is never presented. The words marriage, wedding, husband, wife, do not occur once in these books.”  It is not surprising why so many Americans today reject the biblical view of the world (let alone history and family).
An excerpt from Dr. Stephen K. McDowell, co-founder, and President of the Providence Foundation, wrote:
The social studies texts frequently presented 'role models' but 'not one contemporary role model is conservative and male.' High school U.S. history texts almost completely ignored major religious events of the past 200 years and there was “constant omission of reference to the large role that religion has always played in American life.' This was true for elementary texts as well. In one second grade history book, 30 pages were given to the Pilgrims, but they were “described entirely without any reference to religion.” At the end of the first year they observed a day of Thanksgiving, but no mention is made of the fact that they gave thanks to God.
Christian bias via exclusion continues in current textbooks. For example, one recent history text quotes the Mayflower Compact: 'We whose names are under-written … do by these presents solemnly and mutually in the presence of God, and one of another, covenant and combine our selves together into a civil body politick.' What was omitted from this important historical document? Their clear Christian motive: “for the glory of God, and advancement of the Christian faith and honor of our king and country, a voyage to plant the first colonie in the Northern parts of Virginia.”
Bias is not only expressed by exclusion but also by changing the meaning of a text or writing. One U.S. History Advanced Placement textbook summarizes the Second Amendment as, "The people have the right to keep and bear arms in a state militia,” which is an inaccurate meaning of the amendment which clearly states, "the right of the people to keep and bear arms shall not be infringed." This same text says the First Amendment gives us a "separation of church and state," failing to explain this amendment does not separate God from government or religious ideas from public life. Rather, it acknowledges a jurisdictional separation between the institution of civil government and the institution of the church.
Misrepresenting motives is another means of bias. Under the heading 'Roots of American Government,' a popular seventh-grade Houghton Mifflin Social Studies textbook expounds: 'Enlightenment thinkers in the American Colonies were excited. Here they were, the first people in history to have the chance to create an entirely new government based on Enlightenment Principles.' However, America was not created by Enlightenment thinkers on Enlightenment ideas, but according to John Adams, the general principles on which the fathers achieved independence were … the general principles of Christianity.'
This is confirmed in a study done on the influence of Enlightenment thinkers on the political ideas of the Founding Fathers. Professor Donald Lutz conducted an exhaustive ten-year research of about 15,000 political documents of the Founders’ Era, recording every reference our Founders made to other sources. By far, the most quoted source of their political ideas was the Bible, 34% of citations, and about 50% of the other citations came from men with a biblical worldview.
Some texts teach direct lies, like a high school history textbook published by Pearson that teaches Trump is mentally ill and his supporters are racists. In other texts the Founders of America are often presented as atheists, agnostics, or secularists who wanted no religious influence in public life, when in fact, all but a couple of the Signers of the Declaration and two or three members of the Constitutional Convention were orthodox Christians who believed the foundation of free nations rests on the Christian faith."
It is the above-mentioned analysis on education that feeds into the most common misconceptions and errors; of replacing traditional thought and history which was considered normal daily prior to 1900. I feel this is the most harmful to developing an accurate history and historical interpretation of the early American encounters upon which the course has focused. But of course this is just one opinion of many out there.
Daniel L. Smith
 Beliles, Mark A., and Stephen K. McDowell. America's Providential History: Including Biblical Principles of Education, Government, Politics, Economics, and Family Life, 253. 1989.
 Field, Peter S. 2001. ""the Transformation of Genius into Practical Power": Relph Waldo Emerson and the Public Lecture." Journal of the Early Republic 21 (3) (Fall): 467-493.
 Foster, Marshall, and Mary-Elaine Swanson. The American Covenant: The Untold Story, xvii. Mayflower Inst, 1983.
 Beliles and McDowell, 250-251.
 Paul C. Vitz, Censorship, Evidence of Bias in Our Children’s Textbooks, Ann Arbor, Mich.: Servant Books, 1986, p. 1.
 Vitz, 1.
 McDowell, Stephen K. "A Nation at Risk: Changing Textbooks Reveal the Secularization of American Education." Providence Foundation. Accessed February 13, 2021. https://providencefoundation.com/a-nation-at-risk-changing-textbooks-reveal-the-secularization-of-american-education/.