Slaveholding Southerners first began moving to California en masse in 1849, at the start of the gold rush. Over the next several years, they’d bring an estimated 500 to 1,500 enslaved African Americans into California, mostly to labor in the gold diggings. This sparked the fantasies of proslavery expansionists like Henry Wise in Virginia, who predicted that his state alone would make $1 billion from the sale of enslaved people into California’s gold country. The prediction was obviously ludicrous, but it pointed to a very real proslavery ambition for the West.

Other slaveholders came to realize that the real prize in California wasn’t necessarily its gold but rather its newly opened congressional seats. California came into the Union as a free state in 1850, and this stirred something of an existential crisis for slaveholding radicals like John C. Calhoun, who predicted a slow and painful political death for the South, now that it had seemingly lost the West to free labor. And yet nothing of the sort came to pass. Almost immediately, William Gwin seized the reins of power in California. Gwin continued to own and operate a Mississippi plantation with about two hundred enslaved black people at the same time he represented California in the US Senate.

And there’s the rub: sure, California’s constitution technically outlawed slavery, but so long as slaveholders and their friends controlled the political apparatus there, California could never really be counted among the other free states. In fact, through the 1850s, California’s lawmakers sided with the South on most of the major issues of the day, including several measures to expand slavery across the American West. This was a major political and ideological victory for slaveholders. It basically proved that the politics of slavery could survive on nominally free soil.

Slaveholders discovered pretty quickly that if they wanted to own the labor of others in the American West, they didn’t need to import enslaved black people from the South. There was a ready-made slave economy in the form of Native American captives and indebted mestizo peasants. Thousands and thousands of them labored in various forms of bondage in the Southwest, across Utah, New Mexico, Arizona, and California. These bonded Native American laborers were far cheaper than enslaved African Americans. White Southerners didn’t need to transform the West into slave country; it was slave country already.

That said, when white Southerners encountered these enslaved Native Americans in the West, they often feigned shock and outrage at their treatment. John C. Calhoun and Jefferson Davis, among a bunch of other Southern planters, presented debt peonage in New Mexico as a sort of foil to their own system of plantation slavery. To loosely paraphrase, they said, “Oh my goodness, look at how these poor enslaved peasants are being treated in New Mexico. We would never handle our black slaves in a similar manner.”

Their pearl-clutching shouldn’t have fooled anyone, though. Because every time Whigs or Republicans in Congress attempted to outlaw debt peonage in the Southwest, Southerners rallied against the measures. They did so because congressional Southerners knew that an attack on one type of slavery could easily extend to another. Once the domino of debt peonage in the Southwest fell to a federal antislavery law, their own system of bondage in the South might be next. They succeeded in blocking every one of these anti-peonage bills during the late 1840s and 1850s.

We need to understand the history of American slavery in a transcontinental, rather than a strictly regional, frame. That’s largely how slaveholders themselves thought of these various types of bondage in the antebellum United States: mutually supporting systems that ran from the coast of South Carolina in one direction, to the shores of the Pacific in the other. The South’s so-called peculiar institution wasn’t so peculiar after all.

Northerners wanted a railroad that ran exclusively over free soil to bind their free-labor economy to the Pacific Northwest. Southerners, on the other hand, wanted a railroad that ran across the slave states and into the territories of the Southwest, with a terminus in Southern California. That railroad, they argued, would help carry cotton across the continent and, ultimately, across the Pacific to the mass market of China. Cotton was America’s leading export to China for much of the antebellum period, so there was some logic in Southern fantasies about the Pacific trade.

Southerners also believed that a transcontinental railroad would help carry slaveholders, along with their black laborers, into the American Southwest, where they could further entrench their political influence. So the stakes were enormously high for whichever section — North or South — that was able to fulfill its vision for the Pacific railroad.

Neither Northerners nor Southerners were able to build the railroad prior to the Civil War. The issue became too hot to touch by the late 1850s. But slaveholders achieved the next closest thing by constructing the nation’s major overland mail road along a far southern route. It was called the Butterfield Overland Mail Road, and it was a huge coup for slaveholding expansionists, a number of whom used the road to travel westward across the country.

It only ran for a few years before secession and the Civil War killed it. But at the time, it was a cause célèbre and another example of how slaveholders enacted their expansionist agenda for the Far West.

We hear a lot about the Southern fixation on states’ rights. But what we should remember is that even the most dogmatic, small-government, not-in-my-backyard, strict constructionists — guys like John C. Calhoun — were perfectly comfortable accepting favors from the federal government when it suited their interests. Southerners, who touted their states’ rights bona fides, routinely embraced federal power in the name of slaveholding expansion. I like to think of their position on the matter as “states’ rights with benefits.”

This was especially true when it came to projects in the American West. Slaveholders knew that they needed federal financing to construct the transcontinental railroad of their fantasies, and they welcomed a large congressional appropriation for their Overland Mail Road. Even their more quixotic side projects, like Jefferson Davis’s importation of camels for use in military transport in the Southwest, required outlays of cash from the federal government. Slaveholders required an activist and powerful central state to achieve their expansionist aims in the West.

One of the more perplexing questions of my research was: If Southerners represented such a small slice of the total population in the West, how were they able to achieve a dominant position in the region? For instance, white Southerners never amounted to more than 30 percent of California’s voting population, and yet they triumphed in election after election. How can we explain that? In a lot of ways, West of Slavery is a study in minority rule.

The short answer is that they were often able to convince non-slaveholders to support their proslavery agenda. Generally, the most effective way to do that was through pure, simple, dirty race-baiting. California Democrats were constantly branding their political opponents “abolitionists” (and much worse names). In the process, they effectively convinced a majority of voters that they were the only political party capable of sustaining the rights and privileges of white men.

It didn’t matter that their political opponents, whether Northern Democrats or Republicans, weren’t actually in favor of abolishing slavery. The mere suggestion of antislavery fervor in a California politician was enough to doom his career. Antislavery politics were so unpopular, in fact, that in 1857 the California Republican Party — elsewhere an explicitly antislavery political party — nominated a slaveholder for governor, and he still lost in a landslide because his political party was already tainted in the eyes of California’s white voters. That was the power of anti-black racism in antebellum American politics.