Spain’s experiment with being a “nation of nations” is failing. By fostering separate official languages and regional identities, it has courted division. Today, it is being torn apart as separatists in Catalonia agitate for independence.

This is happening in a country that is prosperous and free. Americans have every reason to consider it a warning.

The lesson for us is all the more stark given that Spain inherited this problem (before arguably making it worse). The United States, on the other hand, has gone out of its way to create it. Building “a cosmopolitan federation of national colonies,” in the words of the influential early 20th century transnationalist Randolph Bourne, has been the object of many U.S. policies for decades.

Especially instructive should be one of the Catalonian separatists’ arguments for leaving Spain: that their region is the wealthiest, and they’d like to stop subsidizing the rest. As countless voices on the left and right have been warning for some time, dividing a country into ethnic groups through “multiculturalism” militates against the transfer payments on which modern welfare societies depend.

Or, as Trevor Phillips, a British Labour politician, put it in an important pamphlet last year: “even those of us on the progressive wing of politics must now surely accept that in the conditions of today’s society, our reflex defence of … separate communities is actually undermining one of the most cherished of left-wing values—social solidarity.”

Many studies back this view. One done at Harvard in 2003 found that ethnic and linguistic “fractionalization” in a society “is highly negatively correlated with GDP per capita growth, schooling and telephones per capita” and many other social goods.

Ethnic and linguistic fractionalization is what Spain promoted after it became a democracy upon the death of the dictator Francisco Franco in 1975. During a nearly 40-year strong-arm rule, Franco had suppressed the use of such languages as Catalan and Basque in the northeast and Galician in the Northwest.

These languages have stubbornly persisted since the early Middle Ages, despite the union of different kingdoms that took place in 1469 when Queen Isabella of Castile and Leon married King Ferdinand of Aragon.

That is Spain’s history. Spanish leaders reacted to Franco’s dictatorship with a pendulum swing in the opposite direction. The 1978 Constitution gave 17 autonomous regions power over education and language. Basque, Catalan and Galician were given co-official status with Castilian in their respective regions. Socialist leader Pedro Sanchez reaffirmed last month that Spain would remain a “nation of nations.”

American history has been the opposite. The founders knew the new country they were building would attract immigrants — as it had already done in their time. Their consensus was that Americans would be able to keep their republic only if newcomers adopted the values the framers were nurturing.

George Washington wrote of immigrants that he hoped that “by an intermixture with our people, they, or their descendants, get assimilated to our customs, measures, and laws: in a word, soon become one people.” For Alexander Hamilton, “the safety of a republic depends essentially on the energy of a common national sentiment; on a uniformity of principles and habits … and on the love of country.” Lincoln and some of American’s best writers, such Emerson and Melville, also referred to these ideals.

At the turn of the last century, self-declared transnationalist intellectuals such as Bourne posited the opposite view. “[T]here are two ideals of American nationalism,” he wrote in 1916. “One is that of the traditional melting pot, the other is that of a co-operation of cultures.”

Bourne and his allies were defeated in the court of public opinion by a bipartisan group of assimilationists that included Democrats such as Woodrow Wilson and Republicans such as Teddy Roosevelt. The latter stated the Founder’s contract in this manner: “We should insist that if the immigrant who comes here in good faith becomes an American and assimilates himself to us, he shall be treated on an exact equality with everyone else.”

But the transnationalists found fertile soil in academia, and reappeared later.

In the ‘70s, the Office of Management and Budget began to divide the country into abstract ethnic groups. Hispanics and Asians were added as categories to the Census in 1980. Last year, the Obama Administration proposed adding MENA (for Middle East and North Africa).

The people in question initially resist being forced into these categories. But as videos of the 2015 Census brainstorming meetings that led to the MENA proposals make clear, leaders of special-interest groups argue that government benefits will entice acceptance in the end. School-based instruction championing “cultural retention” and discouraging inter-cultural mixing through “cultural appropriation” shaming will take care of the rest.

In 1997, T. Alexander Aleinikoff, a senior official in the Clinton administration’s Immigration and Naturalization Service, wrote a clarifying article — in which he favorably quoted Bourne — explaining that the task of policy was to promote an America made up of “constituent groups.” 

“The increasing and resilient diversity — the polyethnicism — of the United States is a current and future fact,” he wrote. What is needed, he added, was “policies that foster a nation at peace with its constituent groups and groups that identify with the nation.”

Catalonia is showing us every day that this contradiction, like many others, does not work.