Many factors have been suggested to explain the explosion in Black protest and Black rage over the past two years on college campuses and in cities like Ferguson, Baltimore, and Milwaukee: racist police, insensitive college administrators, bigoted White students, pervasive “micro-aggressions,” the stigma-creating effect of racial preference policies, among others.

But most such factors fail to answer the crucial “why now?” question. It is a fundamental principle of social science analysis, as well as of simple common sense, that change cannot be adequately explained by a “constant.” If the price of gasoline goes up it is not much of an explanation to say that the gas station owners and the oil companies must be trying to earn more profit. Under a free market system market participants are almost always trying to maximize their profits, so if gasoline prices rise (or fall) some other factor besides changes in profit motive must be responsible for the price increase or decrease.

Almost all of the factors typically mentioned to explain recent racial upheavals are “constants” that existed just as much — or to a greater degree — five, ten, or twenty years ago. There is no credible evidence that America’s police have become more racist, that White college students are more bigoted or more “micro-aggressive” than they used to be, that college administrators and college presidents are more insensitive to Black concerns, or that there has been an increase in hostility to Black aspirations either on college campuses or in America’s cities. Something clearly has changed, but it is not to be found in the factors most commentators have focused upon.

Related: How Student Protesters Cheat Themselves

What clearly has changed is the level of Black frustration and disappointment in the closing years of Barack Obama’s administration. And to explain it we must understand what is sometimes called the “Tocqueville Effect” and what social scientists in the 1950s began to describe as frustration born of an unfulfilled “revolution of rising expectations.” Whatever else one might say about Barack Obama’s two victories in his campaigns for the U.S. presidency, they raised the hope, pride, and aspirations of tens of millions of Black Americans in addition to that of many non-Blacks as well. “Hope and change” was the dominant theme of his White House quest, and for many — including the Nobel peace prize committee — his campaign slogans were the source of great expectations.

Whatever else one might say about Barack Obama’s two victories in his campaigns for the U.S. presidency, they raised the hope, pride, and aspirations of tens of millions of Black Americans in addition to that of many non-Blacks as well. “Hope and change” was the dominant theme of his White House quest, and for many — including the Nobel peace prize committee — his campaign slogans were the source of great expectations.

For many Black Americans the election of the first U.S. Black president was euphoric. A pervasive sense of promise and the expectations for fundamental change were everywhere. A new day and a new dawn were upon us. Here, for instance, is a memoir written by a family friend who watched the presidential election returns the night of November 4, 2008 as they were telecast on a large overhead screen in the heart of New York City’s Harlem:

The night Obama was elected for the first time I stood in Harlem in the Adam Clayton Powell State Office Building Square with thousands of Harlemites watching the huge television screen mounted above our heads. … I was awed at the many black men who wept openly. Parents lifted small children in the air and told them to remember this day in history. Some people knelt in prayer. I just felt I finally had personally gotten back at all those who had violated, abused or hated my existence because of the color of my skin. A European media group … approached me because I obviously was an older woman who had experienced more racism than those younger celebrating around me. They wanted to interview me. Though I tried, I could not speak an intelligible sentence, I was too overcome with emotion. … It was a glorious, victorious night! I had lived to see a needed change in this country. My hopes were high for change.

A European media group … approached me because I obviously was an older woman who had experienced more racism than those younger celebrating around me. They wanted to interview me. Though I tried I could not speak an intelligible sentence, I was too overcome with emotion … It was a glorious, victorious night! I had lived to see a needed change in this country. My hopes were high for change.

With hopes raised to such exalted heights, it is no surprise that disappointment would eventually set in. For most Black people, life during the Obama years went on pretty much as it had, with gradually mounting frustration and anger the inevitable result. Even after six years of the Obama presidency, there was little if any fundamental change in the Black standard of living, Black social mobility, Black achievement in the nation’s school system, Black/White race relations, or improvements in the stability and solidarity of Black family ties.

Related: How Yale Tries to Dodge New Protests

The anger and frustration that resulted from dashed hopes and failed dreams led to a situation whereby minor irritants previously endured. A college building named after an early 20^th century U.S. president who shared the White southern view of race relations typical of his time suddenly became intolerable outrages and symbols of extreme and painful oppression.

What was previously viewed as rare and hardly typical cases of rogue cops gunning down innocent and non-threatening Black men came to be identified as an all-pervasive feature of a Black-hating, Black-oppressing, White racist society. Rioting, looting, seizure of college buildings, and the issuance of a host of non-negotiable demands for redress came to be seen by significant numbers of Black people and their White leftist supporters as the understandable — and perhaps even justifiable — response to such provocations.

People who are angry, frustrated, and disappointed often discharge their negative emotions on objects unrelated to the real source of their actual distress. Someone who has had a fight with his boss at work comes home, kicks the cat blocking the path to his favorite easy chair, and screams at his young son for leaving his bicycle in the driveway.

A similar kind of displaced anger and frustration, I believe, was a hidden factor behind much of the heightened racial resentment and Black rage that we have seen since the summer of 2014 on many college campuses and in several U.S. cities. Growing frustration over unrealistic hopes was the “non-constant,” I believe, that helps explain the otherwise inexplicable change in Black behavior. An increase in White racism — the explanation so beloved by the left — explains none of these developments since no such increase has ever been demonstrated and is hardly likely to have occurred.

This situation was in many ways a repeat of the social dynamic that existed in several of the inner-cities of America during the “riot years” of the mid and late 1960s. Then too there was a “revolution of rising expectations” among many Black Americans, one triggered by the unprecedented legislative victories in civil rights during Lyndon Johnson’s presidency. Passage of the 1964 Civil Rights Act, which prohibited racial discrimination in many areas of American life, was seen as a milestone in the Black quest for human dignity and equal rights.

Areas covered in its reach included private and public employment, educational institutions receiving government aid, and private businesses deemed to be “public accommodations” like restaurants and hotels. Hopes were also raised the following year by the passage of the 1965 Voting Rights Act, which assured Blacks the right to vote throughout America, a right effectively denied to them in many of the states of the Old Confederacy.

The passage of these laws, the injustices to which they drew attention, and the hype surrounding their claimed benefits by their most influential supporters led to both a) an exaggerated expectation of immediate positive change, and b) a heightened sensitivity to remaining problems and injustices that the laws did not reach. This combination proved explosive in terms of triggering Black frustration and Black rage that in the years between 1965 and 1969 led to serious Black riots in over a hundred U.S. cities. Paradoxical — and incomprehensible — as it seemed to many, it was precisely in those years in which the social, legal, and economic conditions of Black people advanced most rapidly that Black anger, frustration, and violent behavior reached their peak.

The Tocqueville Effect

One person who would not have been surprised by this 60s-era development was Alexis de Tocqueville, who in his study of the French Revolution first described the relationship between rapidly accelerating expectations and the consequences that often follow from them in terms of frustration, heightened sensitivities, and outwardly directed anger and violence. “It was precisely in those parts of France where there had been most improvements that popular discontent ran highest,” Tocqueville explained about France’s bloody revolution. “This may seem illogical,” he went on, “but history is full of such paradoxes.

Patiently endured so long as it seemed beyond redress, a grievance comes to appear intolerable once the possibility of removing it crosses men’s minds. For the mere fact that certain abuses have been remedied draws attention to the others and they now appear more galling; people may suffer less, but their sensibility is exacerbated. At the height of its power feudalism did not inspire so much hatred as it did on the eve of its eclipse. In the reign of Louis XVI the most trivial pinpricks of arbitrary power caused more resentment than the thoroughgoing despotism of Louis XIV.” (Alexis de Tocqueville, The Old Regime and the French Revolution.)

Revolutions of rising expectations are dangerous affairs and may have various causes. The one of the 1960s in America was produced by an array of factors similar to that of late 18^th century France but quite different from that of the Obama years. But whatever their source, greatly exaggerated hopes for change and improvement are always in danger of leading to great disappointment and frustration, heightened dissatisfaction with one’s lot in life, and a gross reduction in one’s overall sense of happiness and wellbeing. These in turn can lead to political instability, uncontrolled anger, and often violent social unrest.

It is this dynamic, I believe, which helps to explain much of the racial turmoil we have seen of late on college campuses and in many of our cities, and it is this same dynamic which explains why such seemingly minor irritants as a politically incorrect Halloween costume or a tasteless theme-party at a college fraternity house can unleash such immense hatred, pain, and rage. Tocqueville would have understood it all very well.