American teachers are angry.

They have taken to the streets in West Virginia, Oklahoma, Kentucky, Arizona, Colorado — and more recently in North Carolina. Dissent is building in Louisiana and Nevada, too.

But while the protests are spreading this year, the underlying conflict between public school employees and policymakers has roots in decisions made during the last recession, when states and local districts short of cash curtailed education spending for the first time in decades.

This had a pronounced effect on school staffing, with layoffs hitting many states. Districts cut support staff as well as regular classroom teachers. In North Carolina, the number of teachers is down 5 percent since peaking in 2009, while the number of teaching assistants is 28 percent lower. And teacher pay stagnated nonetheless.

Moreover, the recovery that has lifted the private economy has not quite restored school spending to pre-recession levels, especially in states run by fiscal conservatives determined to hold the line on government spending.