The Quebecers in Canada. The Catalan in Spain. The Taiwanese in China. These are a handful of groups out of many that have been vying for secession for years. And in the age of President Trump, even California has called for its own Calexit.

Yet though it’s easy to say, “Scotland wants to secede because of Brexit,” or “California wants to secede because of Trump,” the reason so few separatist movements bear fruit is because the motivations for a true secession—and the conditions which allow it—are unique and longstanding.

Political Sociologist Michael Hechter has explored what the ingredients to a true secession are. His conclusion: secession doesn’t come from one event, but is borne of economic disparities, identity crises, legislative failure, and bad blood.

Different economic interests: In theory, nations work for the betterment of their populations. But if different regions feel that their contributions outweigh their benefits (as was the popular sentiment in Brexit, substantiated or not), calls for separation naturally follow.

Cultural identity: As with any major decision, there is an emotional component. A nation’s identity isn’t purely (or even necessarily mostly) tied to economic shared interests. Rather, it’s a shared sense of affinity and similarity. There are numerous ways a shared cultural identity can form—and numerous ways it can fracture.

Hechter gives the example of two theoretical industrial populations, both with an equal number of Muslims and Hindus. In Region 1, managers are as likely to be Hindu as Muslim. In Region 2, managers are far more likely to be Muslim than Hindu. Despite a shared industry, history, geography, and day-to-day exposure, Region 2 is much more likely to have deep divisions.

Alienation: The intense reactions to former President Obama (civil unrest, an attempt by Texas to secede) and now President Trump (civil unrest, California pondering a future as an independent state) may reflect a sense of personal insult. Hector explains:

Since the individual sense of identity is the feeling of being a worthy person because he fits into a coherent and valued order of things, ego identity depends heavily on affiliations. A threat to the value of those affiliations produces anxiety and defense. For this reason, people often express hostility to those who threaten the correctness of their own behavior and that of the groups to which they belong, and they often do so out of all proportion to the character of the threat that presently confronts them.

A failure to negotiate an alternative. Unless military action is considered an option, seceding states must come to an agreement with their parent state. And as Hechter notes, “If there is one constant in history apart from the universality of death and taxes, it is the reluctance of states to part with territory.” Unless the seceding territory is a clear liability, there are multiple ways—legislative, economic, political—to appease a disgruntled population.

Additionally, secession isn’t planned for in the formation of a country. As Jon Carson noted when Texas attempted to secede, the country’s constitution gave citizens “the right to change our national government … but they did not provide a right to walk away from it.”