Elections are anticipated the world over in 2019, from India and Israel, Germany and Belgium, to Poland and Ukraine. Still, other countries face broader questions about their leaders’ ability to survive in office; France is racked by countrywide protests, the contentious Brexit deadline approaches for Britain and (if some commentators have it right) the United States may reckon with potential impeachment proceedings.

Questions about leadership turnover will span the world in the new year — and the answers have implications for international partners and rivals alike. What does the research tell us about leadership turnover and international politics?

New leaders can mean new foreign policies

2019 may not be the year with the most global leadership turnover — that honor goes to 1990, which saw 45 new leaders come to power, according to calculations based on the Archigos data on political leaders. But 1990 may not be an outlier; there were 43 new global leaders in 2014. And in 1932, 60 percent of countries saw leadership turnover.

Political scientists have accumulated further evidence that who leads matters for patterns of war, peace and prosperity — see, for instance, a recent special feature in the Journal of Conflict Resolution. But it also matters when leadership changes hands.

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Leadership turnover is important because today’s leaders can’t bind their successors to specific foreign policies. Successive leaders can differ in their (a) desire to uphold international commitments, (b) attitudes about trade and commerce, (c) willingness to provide global public goods, (d) ability to negotiate new treaties and (e) preferences over resorting to war, and foreign policy is an area in which even tightly constrained leaders in democracies have wide latitude.

My research (and research here, here and here) shows these differences in preferences can shape international politics in two ways: after new leaders come to power, when they pursue foreign policies at odds with their predecessors, but also beforehand, when leader change is impending.

1. New leaders can stabilize or upset foreign relations

New leadership can stabilize some aspects of a state’s foreign relations and destabilize others. On the stabilization side, leadership change can reset a country’s damaged reputation, and it’s associated with:

But it’s not all sunshine and light. New preferences at the top also mean uncertainty over what bargains are acceptable in lieu of either trade or shooting wars. Leadership changes are also associated with:

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Some countries take wait-and-see approaches to new leadership in rival countries, but on average uncertainty over a new leader’s preferences creates increased risks of all kinds of costly things we might like to avoid — including war.

2. But changes can happen even before new leaders arrive

What happens after a leadership transition is only part of the story. First, lame-duck leaders with dovish preferences are unlikely to initiate international conflicts, but more hawkish lame ducks are unaffected by the impending loss of office; they carry on much as before.

Second, countries also obsess about potential leader change in rival states: Will the incoming leader be more hawkish or more dovish, and what to do about either of those possibilities? With a more dovish (or simply more reliable) leader waiting in the wings, refusing to negotiate makes sense — this was Soviet Premier Nikita Khrushchev’s likely motivation to walk away from negotiations with the Eisenhower administration. During the 1960 U.S. election, Khrushchev hoped to deny Republicans (read: Richard M. Nixon) a foreign policy victory in the U-2 spy plane crisis that might tip the election away from John F. Kennedy.

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What happens when rivals expect hawkish leadership to come to power? Sometimes, states make concessions to keep friendly (read: dovish) leaders in office; this figured prominently in the U.S. plans to slow NATO expansion ahead of the Russian elections of 1996.

At other times, the shadow of a successor more willing to invest in a war effort — that is, one more difficult to defeat — can open brief windows during which states find it attractive launch a war. The Balkan League, for example, saw the potential for a nationalist revolution in the Ottoman Empire as reason enough to launch the First Balkan War in 1912, before a government that would resist with more vigor might come to power.

There’s reason to be wary about new leaders

Heading into 2019, a key takeaway is that leadership changes can change the course of international relations before and after they occur; successors, especially when rival states have good guesses about their preferences, can cast a long shadow when leadership turnover is in the offing.

Indeed, the logic of preventive conflict before a hawk takes power can impact third-party states, as well. So if a state looking to prey on a neighbor knows that its rival’s next leader is likely to defend that neighbor, then striking now — seizing a window of opportunity — can make sense. When leadership turnover looms, we shouldn’t expect it to shape our world only after the fact. The entire transition period, before and after, can push and pull foreign policies in any number of directions — some more worrying than others.

Scott Wolford is associate professor of government at the University of Texas at Austin. His textbook, “The Politics of the First World War: A Course in Game Theory and International Security,” will be published in spring 2019 by Cambridge University Press. Follow him on Twitter at @thescottwolford.