The 1974 election was really the pivotal event in terms of switching Southern political loyalties. For generations, the generally conservative Southern Democrats had remained in the generally liberal Democratic Party because liberals didn’t mess with the one thing that mattered to them: seniority in Congress and the pork barrel spending that came with it.

Ironically, Republicans strongly contributed to the power of Southern Democrats in Congress. The two brief periods of Republican control in 1946-48 and 1952-54 came largely at the expense of Northern Democrats, thus allowing the Southerners to gain seniority. In the 1950s and 1960s, Southern Democrats chaired many of the most powerful committees in Congress, which they used to funnel federal money to their mostly poor states.

Northern liberals were disgusted by the racist Southerners and even more disgusted by their dependence upon them to maintain control of Congress. But after the huge Democratic victory in 1974 in the wake of Watergate and Nixon’s resignation, the liberals decided that they no longer needed their retrograde Southern brethren.

A number of Southern Democrats were stripped of their committee chairmanships, including Rep. Bob Poage of Texas from the Committee on Agriculture, Rep. F. Edward Hebert of Louisiana from Armed Services, Rep. Wright Patman of Texas from Banking, and Rep. Wilbur Mills of Arkansas from Ways and Means. Additionally, a number of changes were made to the House and Senate rules to diminish the power of Southerners to block legislation, which had impeded civil rights bills for decades.

Suddenly, Southern conservatives had no reason whatsoever to stay in the Democratic Party and they were now highly receptive to Republican outreach. The growing power of African Americans in the Democratic Party in the South also tended to push white conservatives out.

Aiding the Republicans was the growing political involvement of religious conservatives in the wake of the Supreme Court’s decision in Roe v. Wade, which legalized abortion. They felt that their values and religious beliefs were under political assault and they fought back at the ballot box, which mainly benefited Republicans, who actively courted them.

All that was left to complete the Republican takeover of the South was an active ground game. In the mid-1970s there really wasn’t much of a Republican Party in the South. Conservative Southern Democrats generally ran unopposed and frequently voted with Republicans in Congress—except on that critical vote to organize Congress, in which they voted with the liberal Democrats.

The Republican most responsible for turning the South Republican was Rep. Newt Gingrich of Georgia, a Republican elected in 1978. A firebrand, he convinced his party that it was a big mistake to give conservative Southern Democrats an electoral pass because they held precisely those seats most amenable to Republican takeover. Gingrich began pressuring them by recruiting good candidates, helping organize the GOP in the South, raising money, and persuading conservative Democrats to switch parties, which many did.

Aiding the Republican effort was the creation of majority black districts in the South as required by the Voting Rights Act. This tended to dilute the Democratic congressional vote and create swing districts around the central cities where most African Americans lived.

It took a long time for conservative Democrats to retire or become Republicans, for redistricting to improve Republican fortunes and for the party of Abraham Lincoln to make inroads where it had been nonexistent in its entire history. But by 1994, the Gingrich strategy paid off and Republicans took control of Congress.

Just as Democrats had depended on the South to maintain their congressional control for generations, Republicans now depend on that region to maintain theirs. This has made the GOP ever more sensitive to issues that especially resonate with Southerners—abortion, gun control, low taxes and a hard line on immigration.

In the process, the liberal wing of the Republican Party completely ceased to exist. Just as all conservative Democrats became Republicans, all liberal Republicans became Democrats. Thus for the first time in American history, our two major parties are ideologically uniform—all the conservatives are in one party and all the liberals are in the other.

Since the GOP is now vitally dependent on maintaining its position in the South, I believe that the South now controls the Republican Party to a much greater extent than it controls the South. This makes it very hard for a Republican presidential nominee to reach out for moderate and swing voters in the North and West.

In effect, the price Republicans pay for holding Congress, by way of the South, is that its presidential nominees become unelectable. Republicans don’t yet believe this, but when they lose again in 2016, at least some will be forced to accept it.