President Trump wants more “patriotic” American history curriculums. He’s not the first to try. Americans have long been anxious over what schools teach, and this has produced fierce ideological battles over what fills textbooks.

Many Americans believe students directly absorb whatever is written in their textbooks. That makes the stakes over what gets into these books on science, health or history immensely high — an entire generation of Americans stands to be indoctrinated. That perspective, at least, has been the sense of conservative activists in Texas, who for decades have campaigned for more “patriotic” books to ensure the next generation of voters receive, as they see it, the right message.

Since the late 1960s, these activists have become increasingly adept at shaping the character of school history texts. Because of the size of Texas’ textbook market, their activism influenced what was taught to all American children. For publishers, it was not economically viable to write one book to appease campaigners in Texas and a different version to sell elsewhere. The result: Students across the country got books that told U.S. history from the perspective of a small group of White, God-fearing, conservative Texans. Over 20 years, textbook activists shifted the meaning of “patriotic history” from a postwar liberal consensus to a right-wing, colorblind, heteronormative, nationalist retelling of the American story — one that persists today.

For as long as there have been history textbooks, there have been activists trying to change them. Since the landmark 1954 Supreme Court decision in Brown v. Board of Education, which found segregated schooling unconstitutional, conservatives have most vociferously and successfully campaigned for their version of history in textbooks. The accomplishments of the civil rights movement threatened all the social certainties that conservatives held dear. Alongside their resistance to desegregation, conservative activists seized upon the history curriculum because it allowed them a way to control the narrative of the changes America was undergoing.

By the 1970s, the turbulent history of the past two decades had to be included in the textbooks. In Texas, conservative activists transformed their approach, shifting focus from critiquing already-written textbooks toward a wholesale takeover of the bidding and selection process. Most significantly, they targeted the content guidelines, a set of basic instructions given to publishers upon which to base their books.

These guidelines had never been overtly left wing. They had always called for books to be “patriotic” in character. Indeed, with titles such as “The Glorious Republic” or “Land of Promise,” and with covers adorned with bald eagles and fluttering stars and stripes, there was no mistaking them for anti-government propaganda. But the definition of patriotism on which they were based reflected a bipartisan, postwar consensus of liberal internationalism.