How Civil Wars End

As with most civil wars, the war in Yemen is marked by the influence of outside actors. It began in September 2014, when the Iranian-backed Houthis took over the capital Sana’a, and it might well have ended six months later, when the president fled a Houthi advance on Aden. Instead, Saudi Arabia led a coalition of ten Arab countries—supported by the United States—in an air and ground campaign against the Houthis. Since then, the war has ground on, with a new dimension of fighting opening recently between southern secessionist militias—many of which receive support from the United Arab Emirates—and government forces backed by the Saudi coalition. Since taking office, the Trump administration has increased American air strikes in Yemen six fold.

The phenomenon of outside powers supporting different sides in civil wars is not unusual, of course. Civil wars are often beholden to the whims of external forces. It is surprising, however, that the scholarly literature on civil war termination has not addressed systematic changes over time in the ways in which external powers seek to end civil wars.

In a recent article published in International Security, we find that civil war termination varies by time period. We identify three important shifts in recent history. During the Cold War, most civil wars ended with complete defeat for the losing side. After the Cold war, most ended in negotiated settlement. Since the terrorist attacks of 11 September 2001, civil wars still tend to end in negotiation, but not when a terrorist group is involved. Why would the nature of civil war termination vary by time period?