WASHINGTON — There is a basic fact about Syria's civil war that never seems to change: It frustrates any attempt at resolution.
Despite many offensives, peace conferences and foreign interventions, including this week's Turkish incursion into a border town, the only needle that ever seems to move is the one measuring the suffering of Syrians — which only worsens.
Academic research on civil wars, taken together, reveals why. The average such conflict now lasts about a decade, twice as long as Syria's so far. But there are a handful of factors that can make them longer, more violent and harder to stop. Virtually all are present in Syria.
Immune to exhaustion
Most civil wars end when one side loses. Either it is defeated militarily, or it exhausts its weapons or loses popular support and has to give up. About a quarter of civil wars end in a peace deal, often because both sides are exhausted.
That might have happened in Syria: the core combatants — the government and the insurgents who began fighting it in 2011 — are both quite weak and, on their own, cannot sustain the fight for long.
But they are not on their own. Each side is backed by foreign powers — including the United States, Russia, Iran, Saudi Arabia and now Turkey — whose interventions have made Syria an ecosystem with no entropy. In other words, the forces that would normally impede the conflict's inertia are absent, allowing it to continue far longer than it otherwise would.
No winners or losers
Foreign sponsors do not just remove mechanisms for peace. They introduce self-reinforcing mechanisms for ever-intensifying stalemate.
Whenever one side loses ground, its foreign backers increase their involvement, sending supplies or air support to prevent their favored player's defeat. Then that side begins winning, which tends to prompt the other's foreign backers to up their ante as well. Each escalation is a bit stronger than what came before, accelerating the killing without ever changing the war's fundamental balance.
Syria has seen repeated mass, indiscriminate killings of civilians, on all sides. This is not driven just by malice, but by something more powerful: structural incentives.
In most civil wars, the fighting forces depend on popular support to succeed. This "human terrain," as counterinsurgency experts call it, provides all sides with an incentive to protect civilians and minimize atrocities, and has often proved decisive.
Wars like Syria's, in which the government of President Bashar Assad and the opposition rely heavily on foreign support, encourage the precise opposite behavior, according to research by Reed M. Wood, Jacob D. Kathman and Stephen E. Gent, political scientists at, respectively, Arizona State University; the State University of New York at Buffalo; and the University of North Carolina.
Because Syria's combatants rely on foreign sponsors, rather than the local population, they have little incentive to protect civilians.
Peace deals often succeed or fail on the question of who will control military and security forces. In Syria, this may be a question without an answer.
It's not an issue of greed, but of trust. After a war as brutal as Syria's, in which more than 400,000 people have been killed so far, the combatants reasonably fear they will be massacred if the other secures too much power. But a deal that would give the parties equal military power creates a high risk of relapse into war. So does allowing rebels to keep their arms and independence — a lesson the world learned in Libya.
At the same time, there has to be some sort of armed force to restore security and clean up any remaining warlords or militias.
Often, the solution has been for an outside country or organization, such as the United Nations, to send peacekeepers. These forces keep everyone in check during the country's transition to peace and provide basic security in a way that won't spur either side to rearm.