Civil wars don’t always begin with gunfire. Sometimes civil wars begin with learned arguments. In April 1861, Confederate forces shot on Fort Sumter, but at the time even Jefferson Davis, the Confederate president, had doubts about whether the event mattered all that much. It was, he claimed, “either the beginning of a fearful war, or the end of a political contest”; he could not say which. During the decades that preceded the assault on Fort Sumter, complex legal and political fissures had been working their way through the United States, slowly rendering the country ungovernable and opening the path to mass violence.

The US is the middle of another such legal crackup, this time over the question of abortion. The courts today face the crisis American courts faced in the 1850s: is there any way to make laws for a country with furious and widening differences in fundamental values?

This summer, when the US supreme court makes its long-expected decision in Dobbs v Jackson Women’s Health Organization, it will inevitably alienate half the country. In anticipation of the overturning of Roe v Wade, several states have passed draconian anti-abortion laws, in the expectation that they won’t be challenged. Idaho has already imitated the Texas law which allows private citizens to sue anyone who helps a woman procure an abortion, a law that the supreme court has refused to overturn.

Two American blocs are emerging. In the south and parts of the west and midwest, abortion laws are about to return to where they were in the 1950s. The rest of the country has already set itself in opposition to these laws. The division will not stay considerate and respectful, particularly in areas where liberal and conservative states neighbour one another. In anticipation of a post-Roe world and a flood of out-of-state patients, abortion providers have established a series of abortion clinics in Illinois, across the river from more conservative Missouri. Oregon recently invested in a $15m fund for medical refugees traveling from Idaho for abortions.

There are, right from the beginning, two reactions to the new division. The first is the use of force, as in the case of a 26-year-old Texan woman, Lizelle Herrera, who was recently arrested for murder for allegedly self-inducing an abortion. The local district attorney’s office ultimately released her without charge, explaining that “in reviewing applicable Texas law, it is clear that Ms Herrera cannot and should not be prosecuted for the allegation against her”. To be clear, current applicable Texas law doesn’t apply to Herrera’s case. When it does, they will charge people like her with murder. How far will the forces opposing abortion take a custodial approach? Do they want to set up a DEA-style birth police? Any enforcement mechanism will also probably be highly ineffective. After billions of dollars spent on the war on drugs, the average price of a hit of heroin on the street is between $5 and $20. Women with means who want abortions are going to get them.

The second reaction to an America divided along abortion lines will be interstate conflict. Missouri is leading the way here. A recent bill proposed a travel abortion ban, explicitly focused on clinics in Illinois. This looks, on the face of it, like a straight violation of the 14th amendment, but the supreme court is a partisan institution and interpretation of the constitution now follows the partisan affiliation of the justices. They’ll come up with something.

No matter what decision the supreme court makes, civil unrest will follow. Anti-abortion activists will feel that their political system has failed them no matter what the court does. They have sacrificed everything – the dignity and integrity of their party, the value of their national institutions – in the name of getting enough justices on the court to enact this one legal change. If the court upholds Roe v Wade, they will quite naturally feel betrayed. If the court overturns Roe v Wade, they will discover a fact the new Texas law has inadvertently revealed: that the criminalization of abortion doesn’t work. Their basic assumption, that the government can outlaw abortion, is simply untrue. At first, the Texas law appeared to cause abortions to decline by half. But quickly the numbers reasserted themselves. The decline is less that ten percent. Women went out of state or bought chemical abortions. The overturning of Roe v Wade will makes women’s medical treatment more difficult and impersonal and humiliating. It won’t change the abortion rate significantly.

Meanwhile, from the other side, an overturning of Roe v Wade will be experienced as oppression pure and simple, especially given the number of justices appointed by presidents who did not receive the popular vote. In November 1860, five months before Fort Sumter, in the immediate aftermath of Lincoln’s election, a judge in South Carolina announced that the state would no longer register indictments in federal court. Andrew Magrath, in a deliberate act of rejection, removed his judicial robe and folded it over his chair. He would now serve as a justice of his state, not his country. The audience recognized the gravity of the act. As one commentator at the time noted: “Here was a great political movement precipitated, not by bloody encounters in the street or upon the field, but by a deliberate and reasoned act in the most unexpected and conservatives of all places – the United State courtroom.” From that moment on, there were two legal systems. All that remained was the war. A similar breakdown in the legal system of the United States is already apparent.

Needless to say, this entire conflict is futile and stupid. Abortion in the United States is in rapid decline without the negligible effects of criminalization. The number of procedures dipped 19% between 2011 and 2017. If activists want fewer abortions, there are plenty of strategies that are vastly more effective than making them illegal. Canada, which has no federal laws of any kind on abortion, has a fraction of the abortion rate of the US.

But that’s not really the point. Abortion is only a stand in for a fundamental conflict in political vision: morality against policy, community values against personal agency. There are two countries, at least, in the United States. The legal system is only catching up.

• Stephen Marche is the author, most recently, of The Next Civil War: Dispatches from the American Future