In a recent article, I argued that the Republican Party has been captured by a faction whose political psychology makes it highly intransigent and uninterested in compromise. That article focused on the roots of this psychology and how it shapes the Tea Party’s view of its place in American politics. It did not pursue the question of exactly how this capture took place — of how a major political party, once a broad coalition of diverse elements, came to be so dependent on a narrow range of strident voices. This is the question I propose to explore below.

In doing so, we should keep in mind three terms from political science (and much political journalism) — “realignment,” “polarization” and “gridlock.” These concepts are often bandied about as if their connections are obvious, even intuitive. Sometimes, indeed, a writer leaves the impression that they are virtually synonymous. I think this is mistaken, and that it keeps us from appreciating just how strange our present political moment really is.

“Realignment,” for instance, refers to a systematic shift in the patterns of electoral support for a political party. The most spectacular recent example of this is the movement of white Southerners from the Democratic to the Republican Party after the passage of major civil rights laws in the mid-1960s. Not coincidentally, this event was critically important for the evolution of today’s Republican Party.

After the Civil War and the collapse of Reconstruction in the 1870s, the identification of white Southerners as Democrats was so stubborn and pervasive as to make the region into the “solid South” – solidly Democratic, that is. Despite this well-known fact, there is reason to suspect that the South’s Democratic alliance was always a bit uneasy. As the Gilded Age gave way to the first decades of the 20th century, the electoral identities of the two major parties began to firm up. Outside the South, the Democrats were the party of the cities, with their polyglot populations and unionized workforces. The Republicans drew most of their support from the rural Midwest and the small towns of the North. The Democrats’ appeal was populist, while Republicans extolled the virtues of an ascendant business class: self-sufficiency, propriety, personal responsibility.

It will be immediately evident that the Republican Party was in many ways a more natural fit for the South, which at the time was largely rural and whose white citizens were overwhelmingly Anglo-Saxon Protestants. The South’s class structure, less fluid than that of the industrial and urban North, would have chimed with the more hierarchical strains of Republican politics, and Southern elites had ample reason to prefer the “small government” preached by Republican doctrine. But the legacy of Lincoln’s Republicanism was hard to overcome, and the first serious stirrings of disillusion with the Democratic Party had to wait until 1948. That year, South Carolina Gov. Strom Thurmond, enraged by President Truman’s support for some early civil rights measures, led a walkout of 35 Southern delegates from the Democratic Convention. Thurmond went on to become the presidential nominee of a Southern splinter group, the States’ Rights Democratic Party (better known as “Dixiecrats”), and won four states in the deep South.

The first Republican successes in the South came in the elections of 1952 and 1956, when Dwight Eisenhower won five and eight states, respectively*. These victories, however, were only marginally related to racial politics; Eisenhower’s stature as Supreme Commander of Allied Forces in World War II had a much larger role, as did his party’s virulent anti-communism. Nixon held only five of these states in 1960.

The real turning point came in 1964. After passage of the Civil Rights Act, Barry Goldwater’s conservative campaign, with its emphasis on limited government and states’ rights, carried five Southern states, four of which had not been won by a Republican in the 20th century. No Democratic presidential candidate has won a majority of Southern states since, with the single exception of former Georgia Gov. Jimmy Carter’s 1976 campaign. The South is now the most reliably Republican region of the country, and supplies the party with most of its Electoral College support.

The South’s realignment explains a lot about our politics. But it doesn’t, in itself, explain one very important fact: why the post-civil rights Republican Party went on to become the monolithically conservative party we have today. We can put this point as a question: Why didn’t the Republican Party end up looking more like the pre-realignment Democrats, with a coalition of Northern moderates and liberals yoked to conservative Southerners? (And the Midwest along for the ride.) In effect, we’re asking how realignment is related to “polarization” — the ideological sorting out that has led to our present party system, in which nearly all moderates and liberals identify as Democrats and nearly all conservatives as Republicans.

It’s important to ask this question for at least two reasons. First, because it highlights the fact that realignment and polarization are analytically distinct concepts — a point often passed over in discussions of this subject. The sudden migration of Southern whites into Republican ranks is obviously connected with polarization; what we need to know is exactly how and why. Which brings us to the second reason. Because the answer we’re led to is so refreshingly old-fashioned and therefore, in today’s intellectual culture, completely counterintuitive: They are connected through the agency of political actors.

In “Rule and Ruin,” his wonderful history of the collapse of Republican moderation, the historian Geoffrey Kabaservice documents the process by which conservative activists remade the Republican Party in their image. (If I could recommend only one book this year to students of American history, it would be this one.) Filling a broad canvas with an enormous wealth of detail, Kabaservice shows us that conservatives always thought of themselves as engaged on two fronts: Moderate Republicans were as much the enemy as liberal Democrats. William Rusher, Bill Buckley’s colleague at National Review, remarked revealingly that the modern conservative movement formed itself “in opposition to the Eisenhower administration.”

One can’t help but admire the tenacity, focus and creativity that conservative activists brought to their task. They transformed the Republican Party at every level: from the grass roots, where they assumed control of local bodies such as city councils, caucuses and county commissions, to the state and national party machinery. They also built a network of institutions designed to cultivate and publicize conservative ideas. These ranged from relatively sophisticated periodicals and think tanks (National Review, the early Heritage Foundation) to rawer, more demotic facsimiles (the American Spectator, the Cato Institute). Groups such as the Moral Majority arose, especially on the religious right, and new media technologies allowed for the consolidation of conservative voices on talk radio and cable television.

These actions were all part of the same relentless design: to purge the Republican Party of moderate voices and to install conservatives in every position of meaningful power and influence. But they had another side as well. Because as a party shapes itself it also shapes its electorate. And a party engaged in a process of purification, if it wants to continue to win elections, needs a similarly purified electorate.

The realignment of Southern whites must be understood in this context. When they deserted the Democratic Party in the mid-’60s, they presented Republicans with a huge electoral windfall. Republicans then had to decide how to invest this unexpected capital. In doing so they had to balance at least two things: numbers and intensity. Numbers are important, of course — you can’t win elections without them — but it’s an old adage in politics that an intense 51 percent is better than a relaxed 55 percent. The Republican decision to embrace an increasingly radical version of conservatism should be seen, in effect, as an attempt to leverage the intensity and loyalty of their new Southern voters. These qualities were expected to offset the loss of any moderate or liberal supporters who might abandon the party as it lurched to the right.

It was a perfectly rational strategy, and it worked brilliantly. Between 1968 and 1992 — 24 years, an entire generation — Democrats won exactly one presidential election, the post-Watergate campaign of 1976. But after ’92 the strategy began to break down on the national level, due mainly to demographic factors: There simply weren’t enough rural white voters anymore to win presidential elections in a consistent way. But by then the right was fully in control of Republican politics and uninterested in sharing power (or policy) with their moderate brethren. They developed a narrative to counter any suggestion that ideological rigidity was the cause of the party’s losses in national (and, increasingly, statewide) races: the quixotic claim that it had nominated “moderates” unable to bring out the conservative majorities who lurk, abandoned and bereft, in the heartland.

In the meantime the ritual purges have continued — the immediate denunciations, thundered from various media pulpits, whenever a Republican politician utters an unorthodox opinion; the threat (or reality) of primary challenges to silence dissent; the invocation of paranoid fantasies that inflame “the base” and make them ever more agitated and vindictive.

Now, in 2013, we have the politics that 50 years of this process have created. The Democratic Party has fewer conservatives than it once did, but is still a broadly coalitional party with liberal and moderate elements. It controls the coasts, has strength in the industrial Midwest, and is making inroads in the upper, more urbanized South and in Florida. It confronts a Republican Party almost wholly dependent on the interior states of the old Confederacy. (The party continues to win in the mountain and prairie West, but the region is too sparsely populated to provide any real electoral heft.) Because of its demographic weakness, it is more beholden than ever to the intensity of its most extreme voters. This has engendered a death spiral in which it must take increasingly radical positions to drive these voters to the polls, positions that in turn alienate ever larger segments of the population, making these core voters even more crucial — and so on. We have a name these days for the electoral residue produced by this series of increasingly rigorous purifications. We call it “the Tea Party.”

The cry of the hour is that our politics is “dysfunctional” — mired in “gridlock,” all bipartisanship lost. This is of course true, but it must be seen as merely the latest result of the conservative politics of purity. After all, when does a politician, in the normal course of affairs, have a reason to do something? When he thinks it will gain him a vote, or that not doing it will cost him a vote. It follows that politicians have a reason to be bipartisan — to work with the opposition — only when doing so will increase, not decrease, their electoral support. And this can only happen if they potentially share voters with their opposition. But the Republican electorate is now almost as purified as the Republican Party. Not only is it unlikely to support Democratic candidates, it’s virtually certain to punish any Republican politician who works with Democrats. The electoral logic of bipartisanship has collapsed for most Republicans; they have very little to gain, and much to lose, if they practice it. And so they don’t.

Unfortunately, our government isn’t designed to function in these conditions. The peculiarities of our system — a Senate, armed with the filibuster, that gives Wyoming’s 576,000 people as much power as California’s 38,000,000; gerrymandered districts in the House; separate selection of the executive and the legislature; a chronically underfunded elections process, generally in partisan hands and in desperate need of rationalization — simply won’t permit it. What we get instead is paralysis — or worse. The Republican Party, particularly in the House, has turned into the legislative equivalent of North Korea — a political outlier so extreme it has lost the ability to achieve its objectives through normal political means. Its only recourse is to threats (increasingly believable) that it will blow up the system rather than countenance this-or-that lapse from conservative dogma. This was the strategy it pursued in the debt ceiling debacle of 2011, and if firebrands such as Ted Cruz and Mike Lee have their way it will guide the party’s approach to the same issue this fall, and perhaps to government funding (including “Obamacare”) as well. Realignment and polarization have led us to gridlock and instability.

The relentless radicalization of the Republican Party since 1964 is the most important single event in the political history of the United States since the New Deal. It has significantly shaped the course of our government and will continue to do so for the foreseeable future. But this means it has also shaped the individual life of every citizen— the complex amalgam of possibilities and opportunities available (or not) to each of us. The conservative visionaries of the ‘50s and ‘60s wanted a new world. We’re all living in it now.

* The 1928 election is something of an exception to this statement; eight Southern states, offended by Democratic candidate Al Smith’s Catholicism, voted instead for Herbert Hoover. But it seems safe to regard this election as an outlier; FDR won every Southern state in the next four presidential elections.