Even after the unrest in Ferguson has subsided, we’re left with questions about the tension that built up and exploded in the small St. Louis suburb. Among those questions: How did a city where two-thirds of the residents are black elect an almost entirely white city government?  The answer is simple:  Ferguson holds its city elections off-cycle, entirely separate from state and national elections, and that can make all the difference.

People rarely think about the timing of elections. But Missouri’s election rules set the stage for the discontent that has tormented Ferguson this month.  The state requires its cities to hold elections in April, when there are no state or national offices on the ballot to draw voters to the polls.  As a result, voter turnout is very low.  In Ferguson, turnout in the most recent election was an abysmal 12 percent, and best estimates indicate that white residents participate at much higher rates in the city’s elections than black residents. White residents were three times more likely to vote than black residents in the April 2013 municipal election, according to a Washington Post analysis of Catalist data. Suddenly, it is much less surprising that Ferguson elected a white mayor, five out of six white council members, and has a 53-member police force with only three black officers.

The pronounced effects of off-cycle election timing extend far beyond Ferguson.  Researchers Zoltan Hajnal and Jessica Trounstine have shown that cities with low turnout tend to elect fewer minority city council members.

My own research has found that off-cycle election timing increases the political influence of various groups that are highly motivated and well-equipped to mobilize their supporters, such as teachers’ unions in school board elections and police officers and firefighters in city elections. For example, in school districts that hold off-cycle elections, teachers are paid significantly higher salaries than in school districts that hold on-cycle elections. Exactly who wins and who loses from off-cycle election timing differs from place to place, but when elections are off-cycle, small groups can have a big impact on elections—and be rewarded handsomely with favorable public policies.

Moreover, the election timing rules of Missouri and Ferguson are not unusual in the United States.  As of 2012, 21 states required all of their municipal elections to be held off-cycle, and almost all of the remaining states had at least some cities with off-cycle elections.  A mere five states required that municipal elections be held on the same day as national elections.  Off-cycle timing and low turnout in municipal elections are therefore the norm in the United States—not the exception.

If Ferguson’s elections were simply rescheduled to coincide with national elections, turnout in the city’s races would more closely mirror the significantly higher turnout of national races. In California, turnout is a whopping 36 percentage points higher in cities that hold elections on the same day as presidential elections than in cities that hold off-cycle elections. In Minnesota, turnout is 22 percentage points higher in on-cycle school board elections than in off-cycle school board elections. Timing is the most important factor in explaining why turnout is low in some cities and high in others.

While rescheduling local elections would attract a broader, more representative slice of the eligible electorate, and drive policies that more closely reflect the preferences of citizens, there are some downsides. Off-cycle local elections became a standard during the early 20th century, when progressive reformers argued that local issues and policymaking are sufficiently different from state and national ones that the elections should be held separately. Combining local, state and national elections also creates significant administrative hurdles to and exhaustingly long November ballots in even-numbered years. But the benefits of higher turnout and stronger local democracy far outweigh the costs of dealing with those hassles.

The solution may be simple, but the politics of changing local election timing is anything but. The groups that benefit from low turnout lobby hard to keep off-cycle elections in place — and thus to protect their advantage. And legislators charged with setting election schedules listen to those groups, because those on the other side — those who would benefit from a switch to on-cycle elections — are typically unorganized and inactive.

But now, with the spotlight on Ferguson, people are calling for explanations. Ferguson’s warped political structure can be largely explained by a simple electoral rule that locks in low turnout — not just in Ferguson, but in literally thousands of American municipalities and school districts.  It is time for that to change.