The North’s motivation for invading and fighting the War Between the States was partly nationalism and financial (US tariffs meant the South was a captive market for northern manufactures). But the main motivation was the concern that, if states were allowed to secede, that Americans would be too weak to keep dangerous European powers from infringing on American interests in the region, conquering Americans, and eliminating the only republic on the globe. Although nationalism was real in the North, the concern to keep the US growing populous enough to survive European monarchies’ interference was more substantial. They fought for the “Union” more because they cared about Americans remaining a republic, not because they hated secession.
Both Northerners & Southerners referred to the US in the plural until after the war (“the United States are great” not “the United States is great”). Slavery and claims that secession was improper were concerns for only small segments of the US, so it’s anachronistic that modern debates focus on the constitutionality of secession. Constitutionality was used as a fig leaf to justify the true motivations at the time, as can be seen by the pathetic and transparently meritless 1868 opinion by the Supreme Court relating to the constitutionality of secession.
The people who fought the war grew up in an era that was like every other American era until the Cold war in this respect: geopolitics and history was about the struggle between various European colonial powers, especially Britain, France, Spain, and the Netherlands. The Founding Fathers were deathly afraid of disunion because of the weakness of the US as compared to these powers. By 1860, the US was stronger than the empires of Spain, Portugal, and the Netherlands globally, or at least in the hemisphere. But the British Navy was still several times more powerful, and had 10 times the coal production (a measure of industrialization, manufacturing, and ability to support steamships). France’s army was still twenty times larger. Populations were UK: 29M, France 37M, & US 31M, but the UK also had 20M in Canada, Australia, and other colonies, plus 200M in India. The GDP’s of these three powers were roughly equivalent.
Northerners expressed fear that France, through its conquest of Mexico (1861-1867) or the UK could ally with the South against the North long-term. The UK’s great industrial textile industry got its cotton from the South. In combination with Canada (British), either combination could pick off more Northern states or invade.

With the US/UK agreement on a northern border for the US pacific northwest in 1846, the US’ plans to control the area from East Coast to West Coast without interference (colonization) from overseas was in good shape, but not set in stone. Oregon became a state in 1859, and the US Southwest had been annexed in 1845 & 1848 when Texas joined the Union and the US won the resulting war with Mexico. Fedgov conquered and incorporated the Mormons of Utah in the Utah War of 1857-1858.
Monarchism as an ideology (divine right) was in competition with republicanism to the extent that monarchies cooperated in Europe solely with the intention of wiping out republics that had sprouted up in 1848, so that monarchies would no longer have an ideological competitor that weakened the security of the institution. The North feared they could do the same in the Americas, first in Latin America, and then invading the US from Mexico. Their concerns were proven correct in late 1861, when France, Spain, and Britain jointly invaded Mexico, supposedly to collect debts, but then France put a European on the throne of a new Mexican monarchy. And Spain reconquered the Dominican Republic, wiping out a republic. Admittedly, the North’s invasion of the South did nothing to prevent these events. But to politicians like Lincoln, regaining the South would put the US in a position to prevent such things via the Monroe Doctrine. Lincoln was correct, as US intimidation did push France out of Mexico in 1867.
Fighting a brutal war that reduced the population by 2% was a terrible way to maintain the North’s strength. But in 1861 the European powers were not in position to invade the US. According to speeches by Northern politicians such as Lincoln & Seward, the war was seen as a temporary cost that would yield a long-term payoff in creating the precedent that secessions would be punished, so that the US would remain populous, and the North itself wouldn’t split into multiple federations. In Lincoln’s December 1862 State of the Union annual message to Congress, he feared “…how much one huge example of secession, breeding lesser ones indefinitely….” They viewed the war as a painful but necessary investment: endure one major conflict in the 1860s to preserve a powerful, indivisible nation capable of enforcing its hemispheric interests and deterring future foreign encroachment.
Why else would Lincoln feel compelled to prove that a republic can use violence to avoid splitting apart? Can’t each half of a former republic remain republican? It’s not a lack of democracy that is at issue, but the chance of predation, subversion, & bribery (or shared interests) by external actors. Defense treaties are not quite as durable or reliable as sharing a single military & government in common.
If federations always allow member states to secede without cost, but empires don’t, this is one factor that would tend to make federations weaker than empires. This tends to make monarchies seem stronger than republics. Lincoln couldn’t accept that factor, and so didn’t want it to be true of federations. But it is true, and it also tends to make federations grow easier than empires, in that states are willing to join a federation, but not an empire, precisely because they know they’ll have freedom to secede from a federation, as in the UK’s BREXIT from the EU.
In Lincoln’s inane, deceptive, slippery, insubstantial, and confused 1861 inaugural address, he said:
“This issue embraces more than the fate of these United States. It presents to the whole family of man, the question, whether a constitutional republic, or a democracy—a government of the people, by the same people—can, or cannot, maintain its territorial integrity against its own domestic foes. … Is there, in all republics, this inherent, and fatal weakness?”
Unlike the syphilitic, Bible-quoting yet atheist Lincoln, the Declaration of Independence states that the locus of sovereignty is in The People of a state. They have the sovereignty to prevent secession of parts of the state, and they have the sovereignty to form federations with other states, as they did under the Articles of Confederation, and then separately, under the Constitution. States never gave states (or fedgov) authority to prevent them from withdrawing from either federation.
If Lincoln’s fear was that secession would cause wars (balkanization) among the parts of the US that would weaken them, then his choice to fight exactly that kind of war makes no sense, unless he thought it would prevent future generations from doing so.
Northerners didn’t know that continuing the war would be so costly, and once they’d started, the political and emotional cost of giving up without a victory would have been high.
What do we learn from all this?
If the South had seceded not in 1860 but in 1900, when the North was more industrialized and populous than before, and no longer had to fear invasion from European powers, there would have been no Northern fear that Southern secession would lead to conquest of Americans by Europeans. The fear of the North splitting into multiple federations subsequently could have still been an issue. It’s impossible to know if a state would have wanted to secede in that timeline though, since slavery would have already been uneconomical in the South by then.
Lincoln’s goal was to establish a long-lasting precedent that secession from the Union would be crushed with violence. But the US is only indivisible as long as potential seceders believe that the current fedgov is as pathologically homicidal as Lincoln, as unconcerned about the precedent of Lincoln’s assassination, and as capable as Lincoln was of actually blocking secession.
Today, how shall we soothe Americans’ fears, whether they’re in red states or blue states, that Lincoln’s predictions would come to pass after a US National Divorce? Simply assure them that both halves of such a National Divorce would be well able to deter attack. Share our recent essay about this with them. It’s that simple [note that essay is still in its first draft at the time of this writing, but will be improved in the future]. It may be that the blue states will become more than one country, although they might merge with Canada or parts of Canada or Mexico. But such modern, industrialized societies can punish aggression much more than they can provide loot to conquerors, even if small. If the US were in a war with an invading force, of course secession would be treason for as long as the invasion lasts. But in times of peace, secession is self-determination. It’s just home rule – because any part of the US can deter attack.
We hope the essay you’re reading now convinces you that Lincoln’s arguments against secession are unfounded, as long as deterrence remains. Polls show that support for slavery or Jim Crow are negligible. As for tariffs, blue states & red states will be financially OK without sharing a country, as they can continue to trade with each other (and MUST continue to trade with each other, to avoid a supply-chain disaster that even blue states aren’t foolish enough to choose).
Understanding the geopolitics of the 1860’s shows that the North’s invasion of the South has not quite as dastardly as it first appears. Sticking together as a Union served Americans well for a time – certainly it did in the 1770s. But as the land was settled and industrialized, American states matured to the point that they can defend themselves as independent states. This is another argument for secession. History has led to this point.
We still argue that it’s better for red states to stick together in this classic essay though.