Chinese President Xi Jinping and President Barack Obama toast during a State Dinner, Friday, Sept. 25, 2015, in the East Room of the White House in Washington. (AP Photo/Andrew Harnik)

Who wins a bar fight? The person with the most friends at the bar.

Who wins a war? The country that fights alongside the most allies.

This simple intuition provides an overlooked explanation for an important academic controversy. Democracies win almost all of the wars they start and about two-thirds of the wars in which they are the targets. If we push the bar fight analogy a little farther, we can also understand why being a democracy, and seeking a particular type of objective, is helping the U.S. build a large coalition to prepare for potential bar fights in places like Eastern Europe, the Middle East or the South China Sea.

Obama told China to slow down in the South China Sea.

On his November trip the Philippines, President Obama called on China to halt the militarization of conflicts in the South China Sea, where China has been sparring with the U.S. and its allies over islands, navigation rights, and access to natural resources. Obama also announced $250 million in military aid to our allies in the region.

The U.S. is working actively, and successfully, to build large coalitions to support its goals in the South China Sea and elsewhere. By contrast, adversaries like China and Russia largely stand alone in these disputes.

This is counterintuitive in some ways. For many members of the U.S. coalition in Asia, including the Philippines, Vietnam, Indonesia, and Malaysia, China is the nearer neighbor and a rising trade partner. China is likely more economically important to the future of these countries than the U.S. Similarly, Ukraine and the Baltics share a border with Russia, not the United States. So why do these countries (seek to) ally with us?

One answer is that the United States is pursuing public goods — like open sea lanes or territorial integrity — while China and Russia are seeking territory, which is a private good. It’s easier to build a coalition around the pursuit of something that benefits everyone, rather than an asset that must be divided up, often unequally.

Democracies fight for public goods–which brings them allies. 

In new research, we argue that democracies tend to pursue public goods like open sea lanes and respect for existing territorial borders, while autocracies tend to pursue private goods like territory. Democracies fight alongside more partners. Those larger coalitions win conflicts more often. Coalition size predicts democratic victory so strongly that we needn’t look any farther for an explanation. Others have argued that democracies fight better, that democratic soldiers are more motivated to win or that democracies mobilize for war more completely. But the biggest advantage of democracies may be that they simply build larger coalitions.

Yet if everyone benefits from large coalitions, why do democracies end up fighting alongside more friends than autocracies? Do autocrats not know that ganging up on their opponents is a good idea?

Democracies and autocracies often have different goals in going to war. Fighting alongside friends can be costly as well as rewarding. That’s particularly so when the winner is going to have to share the spoils of victory — oil, territory, or access to the strategic and economic resources in a region such as the South China Sea. For China, adding allies would mean diluting the benefits it achieves by prevailing against its adversaries. States seeking to acquire territory or resources for themselves don’t want any more mouths at the trough than they absolutely need. Sometimes a reluctance to share even means that one side is more likely to lose.

In contrast, if a country is fighting for a principle, for the status quo, or for a public good such as free maritime navigation, then more allies cost very little. In the South China Sea, the U.S. is trying to maintain open sea lanes for trade, something that is just about as valuable regardless of whether others also make use of it. The more the merrier!

This logic extends well beyond the South China Sea. Because of the large number of participants in domestic politics, democracies’ core interests are usually best met through public goods (stability, good governance, parks and welfare). Open sea lanes for trade. Stable international borders. Limiting terrorism, genocide, and other potentially contagious social, political, and economic ills.

When democracies go to war for these objectives, they build overwhelming coalitions and they win.

Autocracies fight for themselves–which leaves them isolated. 

Autocracies, on the other hand, must satisfy relatively small numbers of domestic constituents, something better accomplished through private benefits (cash or other dispensations, control over valuable assets). Because of this, autocracies are more likely to see benefit in going to war for private goods like territory or oil. As a result, they’re more likely to keep their coalitions small–and therefore face a greater danger of defeat.

Democracies don’t just win because of who they are, but because of what they want (and what they don’t). As long as states seek things that coalition partners can share, they tend to win and to get their way in world politics.  This in turn creates a powerful and evolving dynamic in world affairs in which being able to share makes states (often democracies) more successful.

Benjamin A.T. Graham is an assistant professor in the School of International Relations at the University of Southern California and co-founder of the Security and Political Economy (SPEC) Lab.

Christopher J. Fariss is the Jeffrey L. Hyde and Sharon D. Hyde and Political Science Board of Visitors Early Career Professor in Political Science and assistant professor in the department of political science at Pennsylvania State University.

Erik Gartzke is professor of political science at the University of California, San Diego, adjunct senior research scholar at Columbia University in the City of New York and is the principal investigator on a Department of Defense Minerva-funded research project on Cross Domain Deterrence.