The news media today are full of stories about efforts across the United States to draw new state and federal legislative districts following the 2010 Census. Even the U.S. Supreme Court waded into that process very early, by agreeing to hear a legal challenge to a congressional redistricting scheme in Texas.

All of this news reflects the truly unprecedented levels of contention associated with the redistricting process this time. As soon as state legislative leaders propose new district maps, opposition swells, culminating in lawsuits and, at times, judicial rulings requiring legislatures to try again. The overall impression is of a process that has spun out of control, driven by narrow partisanship rather than public interest.

"Gerrymandering," the practice of drawing legislative district boundaries so as to maximize partisan advantage, is far from new. Elbridge Gerry, the Massachusetts governor whose name literally became synonymous with the practice, worked his magic to create a salamander-shaped district over two hundred years ago.

The modern era of legislative redistricting began more recently, however, when the U. S. Supreme Court decided a case known as Baker v. Carr in 1962.

The case involved a lawsuit brought by a man named Charles Baker, a Republican who lived in Shelby County, Tennessee, where Memphis is located. He sued the Tennessee Secretary of State, Joe Carr, because the Tennessee state legislature had not redistricted since the 1900 Census.

Thanks to population shifts over the preceding sixty years, Baker's district in Shelby County had roughly ten times as many residents as some of the rural districts with equal representation in the state legislature. The Supreme Court, by a vote of 6-2, found for Baker. In so doing, the Court announced that redistricting was an issue a court could resolve, thereby over-ruling earlier decisions that courts were not competent to decide such political questions.

Two years later, in a pair of decisions known as Wesberry v. Sanders (1964) and Reynolds v. Sims (1964), the Court found that the Constitution required all states to redistrict after each decennial census, and produce equal population districts for all state legislative and federal (i.e. congressional) seats except for those in the U.S. Senate.

These Supreme Court decisions produced a political revolution that dramatically changed the practice of American politics. We continue to grapple with the results today.

Legislative Districts before Baker

This redistricting revolution strove to tackle longstanding social and political issues in America, from the changing rural-urban relationship, racial discrimination, and the agricultural versus industrial foundations of the economy.

And it was a revolution not just in the mostly one-party, racially segregated South of that day. Many of the states of the North and West had also failed to redistrict regularly (often for decades), albeit for somewhat different reasons.

In fact, until the Court handed down its decision in Baker, the most important previous decision had been in an Illinois case known as Colegrove v. Green (1946), where the Court—reflecting its hands-off approach to the question of districting—declined to enter this "political thicket."

Like Tennessee, the Illinois state legislature had stopped redistricting after the census of 1900. Thus, by the time the U.S. Supreme Court handed down its decision in the Colegrove case, almost half a century of legislative inaction had passed. By that point, a majority of all Illinoisans lived in Cook County (greater Chicago), but they had nothing like half of the seats in the general assembly or in the state's congressional delegation.

The origins of that peculiar state of affairs in the North and West had to do with three streams of migration to the cities there after 1870. The first consisted of the so-called "new immigration" from southern and eastern Europe. That mass movement of people greatly swelled the size of America's cities (almost all of them in the North and West) from the 1880s through 1915.

And then, just as that stream of immigration was cut off by World War I and postwar laws restricting immigration, a second stream of migration to America's urban centers began. This second mass movement of people was an internal one. It consisted primarily of southern blacks moving north and west to cities such as New York, Cleveland, Detroit, Chicago and Los Angeles, in search of more economic opportunity and more legal and political equality.

These two streams of people and a third—the much more gradual movement from the 1870s through the 1940s of native-born whites from the countryside to towns and cities—made the USA a predominantly urban society by the 1940s.

Had state legislatures in the North and West faithfully redrawn legislative districts to keep up with those major shifts in population, no constitutional question would have arisen. In most cases, however, the state legislatures failed to act. Political boundaries were not usually redrawn after the turn of the twentieth century and districts were not divided into blocks of roughly equal population.

As a result, the voting power of those living in growing urban districts was numerically diluted while the voting power of their rural, largely native-born white counterparts was correspondingly enhanced. State legislatures, dominated by rural interests (because the country had once been almost entirely rural) refused to grant concessions needed to achieve more equal district sizes in terms of population.

Resistance to reapportioning seats in the U.S. House of Representatives also grew after 1911, when Congress fixed the total membership of that body at 435.

Up to that point the size of the House had grown as population did. Thereafter, reapportionment became much more of a zero-sum game in which states with growing populations gained seats and those with stable or shrinking populations lost seats. Drawing new lines for congressional districts in that latter context also fed opposition to reapportionment.

Such resistance eventually produced some very bad results. In Illinois, for example, by 1946 residents of Cook County paid 53% of the state's taxes. And the economic importance of Chicago to the state of Illinois greatly exceeded the fraction of the Illinois state legislature representing that city's residents.

Political corruption developed in consequence. The only way Chicagoans could exert influence in the legislature proportionate to the city's economic importance and population size was through the use of money. As one seasoned political journalist, John Gunther, concluded in 1946, "the only way Chicago can operate in the legislature at all is to try to buy it."

Despite these political deformities, the social, cultural and racial gaps were so wide between the minority living in rural areas (usually native born whites) and the rapidly growing majority of urban dwellers (often newcomers to the state, immigrants from southern and eastern Europe, and migrant blacks from the South) that rural residents and lawmakers feared surrendering their control over the legislature to Chicago.

That basic split only deepened during the 1930s and 1940s, when Chicago became one of the most strongly Democratic cities in the country in the context of Franklin Roosevelt's New Deal policies. The rest of Illinois remained the Land of Lincoln, a state in which the rural areas were as strongly Republican as those of any northern or western state in the nation.

After the 1930s, therefore, redistricting meant not only transferring political power to the newcomers in the city; it also often meant transferring control of the legislature from the Republicans to the Democrats. In Illinois, as was true elsewhere in the North and West during the heyday of the New Deal, the last remaining bastion of GOP control was the state government, which Republicans tried very hard to hang onto.

Added to that source of resistance was the enduring importance of agriculture to the economic life of northern states like Illinois. The fraction of the population directly employed in farming fell steadily after the 1870s, but not the volume of crops or their dollar value. Instead, ever more agricultural commodities were produced by ever fewer people.

Thus, after the 1930s, redistricting also implied creating a situation in which agricultural interests would likely have been under-represented in the state's general assembly in terms of farming's economic importance to the state. Trading one form of economic under-representation (the cities') for another (farming areas') actively discouraged redistricting.

To make matters worse, the longer state legislatures waited to redistrict, the more drastic would be the resulting shift in political power, and the harder that change would be to bring about. Resistance to redistricting in the North and West hardened in the 1930s and 1940s.

And even though such a shift in theory was easier in the South, because few outsiders had moved into the region's handful of real cities from the 1870s through the 1940s, the one-party nature of Southern politics at that time fed resistance to change there, because the gradually growing Republican population in Dixie then was almost entirely metropolitan.

There was, of course, a racial dimension to this situation in the South. Rural areas there in 1900 tended to have more black residents than urban areas did, but as blacks migrated to Dixie's cities and larger towns over the following sixty years, that balance shifted somewhat.

If Southern blacks in the future were to gain greater access to the ballot, redistricting implied increasing their political power even more. In that respect, the northern and southern states were more alike than different.

Revolutionizing the Political Landscape: Baker and the 1960s

As the inability of the state legislatures to address the problem of urban underrepresentation grew, and efforts intensified to dismantle the racial segregation system in the South that kept most blacks there from voting, the U.S. Supreme Court was eventually prompted to act as it did in Baker and subsequent, related cases.

The justices were very conscious that they were doing some truly momentous. Chief Justice Earl Warren described the Baker decision in particular as the most important of his time on the Court (1954-1969).

In that case, Associate Justice William Brennan wrote the opinion for six justices. It found six criteria applied in deciding whether an issue constituted a political question that the Court could not resolve. All six involved separation of powers issues among the three branches of the federal government rather than federalism concerns (i.e., the federal government's relationship with the states).

The Court concluded that the Constitution did not commit the reapportionment issue exclusively to the other branches of the federal government (legislative and executive) and so courts could, at least in theory, decide such disputes.

That ruling cleared the way for later decisions in Gray v. Sanders (1963) where the Supreme Court applied a "one person, one vote" standard to statewide elections. It also made possible Wesberry v. Sanders (1964) and Reynolds v. Sims (1964), which applied this standard to congressional districts and to both state legislative houses.

The one person, one vote standard seemed to be the only one a court could easily apply, as the dissenters in Baker had warned, and so its emergence was highly likely once the Baker decision was handed down. So, too, did the requirement that reapportionment take place promptly after each decennial census.

Changing social and political conditions in the country after Baker was decided in March 1962 also pushed the Court to apply those legal rules.

Even though there had been a nationally visible civil rights movement since the Montgomery Bus Boycott of 1955-56, that struggle had been contained through 1962. In May 1963, however, it became unmanageable in Birmingham, Alabama. Violent racial confrontation there and elsewhere in the South and the Border States grew sharply thereafter, and spread North and West to cities there with large black populations.

That turn of events put pressure on the Supreme Court to resolve the reapportionment issue swiftly and decisively. Finding that the Constitution required a one person, one vote standard and reapportionment after each census accomplished that result.

A New Politics: From Baker to Today

With the hindsight of half a century, one can now see clearly that the most important and durable change set in motion by those rulings was the requirement that all state and federal legislative districts must be redrawn after every census to produce districts of approximately equal population.