When it comes to putting big projects together, there’s generally much greater cooperation these days at the local level than there was a generation or two ago. Maybe that’s one reason why American politics has become so polarized.

That may sound like a leap in logic, but sociologist Josh Pacewicz lays out an intriguing case in his book Partisans and Partners. In the old days, politics was used as a tool by local actors concerned with the broader health of the community, he writes, but now that ground has largely been ceded to activists.

Pacewicz, who teaches at Brown University, takes a deep dive into the postwar history of two Midwestern cities. He’s given them fake names, but the outlines of their stories will sound familiar. After World War II, their economies were dominated by a small number of family-owned, often unionized factories. Local politics in turn were dominated by those families and union leaders.

The landscape began to change in the 1970s. For one thing, the federal regulatory approach shifted, allowing more industries to nationalize. Many family-owned companies went away, replaced by firms headquartered elsewhere and run by management less concerned with preserving the health of a given community. At the same time, the federal share of municipal budgets decreased dramatically, forcing community leaders to band together to fight for the scraps.

That created the cooperative culture that now prevails in many places. In order to get grants for, say, a new museum, the local power structure, including the chamber of commerce, developers and nonprofits, has learned to work together, minimizing conflict in order to present a united front to outsiders. This approach has largely made them shy away from partisan politics. They want to keep making deals with other institutions, rather than opening up wounds in political fights. “Those who simultaneously took positions of community leadership and engaged in politics for love of the game are simply gone,” Pacewicz writes.

With community leaders now focused on economic development and placemaking, ideological activists are left in charge of party politics. Instead of an emphasis on pragmatic results, local party leaders are now largely motivated by hot-button issues such as abortion, guns and immigration. This has not only impacted the local political scene, but also affected the types of people who can win nomination to Congress or are chosen as delegates to national party conventions.

At the local level, voters witness a culture that puts a premium on cooperation, Pacewicz says. This makes them wonder why federal politicians can’t similarly put aside their differences and work out deals that are best for the country as a whole. That inability has led more and more voters to grow frustrated and apathetic, and to register as independents. With politics more partisan, people in the center feel like they have nowhere to go.