Of course, the likeliest Republican standard-bearer for 2024 remains former President Donald Trump, who skipped this debate like all the others. But his views obviously hovered over the stage. What’s more, by giving even second-tier candidates a chance to air their conflicts, these exchanges tell us a lot about the range of divisions in the party, as well as their commonality.

Wednesday’s debate did show broad areas of agreement. Despite grumbling in the more extreme flank of the party, support for Israel against Hamas remains the hegemonic position in the GOP; only Vivek Ramaswamy opposed further U.S. aid even as he joined other contenders in offering a bellicose message to Israel that it should “smoke those terrorists.” Similarly, even some candidates’ attacks on each other highlighted a deeper consensus, as when former U.N. Ambassador Nikki Haley and Florida Gov. Ron DeSantis accused each other of being too nice to China. Global climate change received scant attention, while the only tools the debate participants viewed as appropriate to deal with immigration were hard line.

Despite such explicit and tacit agreement, the divisions on display were stark. They reflect core approaches to the world, not just soundbites. The principal split concerned whether to help Ukraine fight Russia or whether to end U.S. aid to that country in favor of focusing on the Mexican border.

Haley and former New Jersey Gov. Chris Christie took a classically (if conservative) internationalist line, arguing that resisting Russian aggression in Europe is the key to preserving U.S. power and avoiding a costlier war later. DeSantis and Ramaswamy argued for pulling back from U.S. support. Yet they did so for different reasons, with DeSantis wanting to focus on countering China and Ramaswamy seemingly arguing for pure isolationism. (In that sense, Ramaswamy may come closest to Trump’s position, which include statements that seem to presage a rapid abandonment of Ukraine and even the possibility of a U.S. exit from NATO.)

This degree of intraparty division about the purpose of foreign policy is reminiscent of earlier eras. In the 1920s, Republican clashes over whether and how to engage with the rest of the world led to a refusal to join the League of Nations combined with a reliance on treaties to manage arms races and even make war illegal — even as nativist sentiment led to a racist anti-immigration law that radically curtailed immigration for a generation.

Perhaps the most illuminating parallel comes from the middle of the 19th century, when U.S. foreign policy turned on a fight among Democrats. In the 1830s and 1840s, Democrats were torn over the breakaway republic of Texas, which had seceded from Mexico. Many Southerners wanted to admit Texas as a state to preserve and extend slavery. Mindful not only of the possibility that annexation would lead to war with Mexico but also of the domestic balance of power, Northern Democrats preferred to do so only if Texas could be accompanied by seizing at least parts of Oregon, then jointly administered with the United Kingdom.

The issue sank the renomination attempts of former president (and party founder) Martin Van Buren, who enjoyed substantial support but opposed annexing Texas and thus could not secure the two-thirds vote needed at the convention. With the favorite out of the way, dark horse James K. Polk secured the nomination through a logroll: promising to expand both southward and in the Pacific Northwest. Polk’s narrow victory in the 1844 presidential election over Henry Clay paved the way not only for the admission of Texas but also for a showdown with Britain over Oregon and a war with Mexico over Texas that resulted in the U.S. conquest of most of the American West.

Those transformations brought not just generational but epochal consequences. Expansion made the United States into a transcontinental country, with its vast Pacific shoreline accelerating its interest in relations with Asia. But expansion also meant that domestic divisions over slavery were accentuated, helping to force the Civil War.

The coming decade in our century could see transformations of similar magnitude in America’s role in the world. After a post-Cold War period that was so peaceful that some proclaimed the end of war, the past decade has seen an acceleration of deaths caused by conflicts. These episodes place new strains on Washington as it seeks to live up to America’s global commitments and responsibilities, especially in the absence of a direct threat to U.S. values and interests like that posed by Nazi Germany or the Soviet Union.

Without such a clear threat or a recent experience of global cataclysm, voters and politicians will see greater latitude to opt out of global engagement. Such a turn inward would have immense effects on international politics: The U.S.-based system would crumble and other powers would seize even larger roles in managing their regions, with potentially deadly results.

Trump and Ramaswamy likely view these potential developments as acceptable, perhaps even welcome. Haley and Christie want to resist them, but in a way that would preserve maximum U.S. freedom of action with much less regard for allies’ concerns or international norms. After all, even Haley favors sending special operations forces into Mexico to go after the drug cartels — a unilateral invasion that would undermine any U.S. admonitions against Russia and other countries for behaving like 19th century rules apply.

Choosing a president always matters. The stakes within the Republican primary, however, highlight just how great the choice before voters in November 2024 could be — whether it will be a choice between rival forms of internationalism or between international engagement and unprecedented retrenchment, with historic consequences.