You could be forgiven, after five years of Syria’s war dominating front pages, for feeling lost.
It is easy to track the war’s toll: It has killed 400,000 people, displaced millions, opened space for the Islamic State, and sucked in foreign powers, including the United States. It is harder to keep track of the how and why. The basics can seem even more confusing than the day-to-day details.
But those basics are crucial to understanding Syria’s war — and they are far more complex than they might initially seem. As last week’s truce appears shaky after American planes bombed Syrian troops, here are straightforward answers to some of the fundamental questions about the conflict: an attempt to explain its origins, the broader context and how it relates to the refugee crisis and the rise of the Islamic State.
1. What is the Syrian civil war?
The war makes more sense if you think of it as four overlapping conflicts.
The core conflict is between forces loyal to President Bashar al-Assad and the rebels who oppose him. Over time, both sides fractured into multiple militias, including local and foreign fighters, but their fundamental disagreement is over whether Mr. Assad’s government should stay in power.
This opened a second conflict: Syria’s ethnic Kurdish minority took up arms amid the chaos. The Kurds carved out a de facto ministate and have gradually taken territory they see as Kurdish — sometimes with backing from the United States, which sees the Kurds as an ally against jihadist groups. While Mr. Assad has not focused on fighting the Kurdish groups, they are opposed by neighboring Turkey, which is in conflict with its own Kurdish minority.
The third conflict involves the Islamic State, also known as ISIS or ISIL, which emerged out of infighting among jihadist groups. In 2014, the Islamic State seized large parts of Syria and Iraq, and it declared that territory its caliphate. The group has no allies and is at war with all other actors in the conflict.
The fourth, and most complex, dynamic may be the crisscrossing foreign interventions, which have grown steadily. Mr. Assad receives vital support from Iran and Russia, as well as the Lebanese militant group Hezbollah. The rebels are backed by the United States and oil-rich Arab states like Saudi Arabia. These foreign powers have different agendas, but all pursue them by ramping up Syria’s violence, helping to perpetuate the war.
2. How did the war happen?
On the surface, the conflict began in 2011 with the Arab Spring. Syrians, like other peoples across the region, rose up peacefully against their authoritarian government. Mr. Assad cracked down violently. Communities took up arms to defend themselves, then fought back in what became a civil war. Some soldiers joined the rebels, but not enough to win.
But that alone does not explain Syria’s disintegration. It is now clear that the state was weak in ways that made it inherently unstable and prone to violence.
The government was dominated by a minority group. Over decades, Syria’s religious and ethnic divides had taken on greater political importance, making the ruling minority fearful and reactive. Mr. Assad had strong support among the military and security services, but not the broader population, making violence more tempting. The instability was deepened by the fact that rural Syrians had moved to cities in large numbers in recent years, driven in part by droughts linked to climate change.
Fighting, once it began, was worsened by several external factors. A decade of war in neighboring Iraq had produced battle-hardened extremist groups that now flowed into Syria. Iraq’s political troubles in 2011 and 2012 helped open space for the Islamic State. During this time, Syria was sucked into the regional power struggle between Iran and Saudi Arabia.
3. Which countries are involved and why?
Five countries are playing a major role in Syria, each with different agendas. Their interventions have locked the war into an ever-worsening stalemate.
Iran was first, sending supplies and soldiers to prop up Mr. Assad. Iran sees Syria as crucial to its regional strategy: It provides access to Lebanon and therefore Hezbollah, a group Tehran uses for regional influence and as a counterweight to Israel, whose nuclear weapons it fears.
Saudi Arabia supported Syria’s rebels in the hopes of replacing Mr. Assad with a friendlier government and of countering Iran’s influence. Saudi Arabia and Iran have been rivals for decades, fighting something like a cold war for regional dominance. (Other Arab states like Jordan, Qatar and the United Arab Emirates have also backed the rebels.)
Their struggle has escalated for several reasons: Iran’s growing power; the regional power vacuum that opened with the fall of Saddam Hussein in 2003 in Iraq; more political vacuums opened by the Arab Spring; a hawkish new king in Saudi Arabia; and Saudi fears that the United States is becoming less hostile toward Iran.
The United States funnels weapons to Syria’s rebels. It did so initially out of opposition to Mr. Assad, a longtime enemy, and later to encourage those groups to fight the Islamic State. The United States has also armed Kurdish groups against the Islamic State.
Turkey sheltered Syrian rebels and ushered in foreign recruits, seeking to undermine and perhaps topple Mr. Assad. Later, the country also acted to counter Syrian Kurdish groups, fearing that they could strengthen Kurdish insurgents in Turkey.
Russia has backed Mr. Assad from the beginning, selling him arms and providing diplomatic cover at the United Nations. Syria is one of Russia’s last remaining allies, and it is where Moscow maintains its only military bases outside the former Soviet Union. Russian forces intervened in 2015, at a time when Mr. Assad appeared to be losing ground.
4. Why is the war so bloody?
There have been atrocities on all sides, but forces loyal to Mr. Assad have committed by far the most. Because his government is so weak — its support base is small and its military has suffered heavy defections — Mr. Assad seems to believe he can regain control only by violently coercing Syrians into submission. That has included using chemical weapons, barrel bombs and starvation.
Because neither Mr. Assad nor the rebels are strong enough to win, the battle lines push back and forth, rolling across communities in waves of destruction that kill thousands but accomplish little else.
Foreign interventions have made those shifting front lines even bloodier and have deepened the stalemate. As a result, the overall violence kills more Syrians without altering the conflict’s underlying dynamics.
The years of chaos have destroyed basic order in Syria. As often happens in lengthy civil wars, militias have filled the vacuum. Their leaders often behave more as warlords, forcibly extracting resources from local communities. This practice has been carried out by rebel militias and some that support the government.
The rise of the Islamic State has worsened all of these trends. The jihadist group has provided another set of shifting battle lines, introduced more warlords, compelled more foreign interventions and, most of all, put communities under its tyrannical, fanatical rule.
5. How did the war become divided by religion?
There is nothing innately religious about Syria’s war, but its broader political forces have played out along religious lines. To understand why, it helps to start about 100 years ago.
After World War I, France took control of the territory of the defeated Ottoman Empire that is now Syria. France ruled through minority groups that would be too small to hold power without outside support. That included Alawites, followers of a branch of Shiite Islam, who joined the military in large numbers. The last French troops left in 1946, and a long period of turmoil followed. Syria’s military consolidated power in a 1970 coup led by Hafez al-Assad, an Alawite general and the father of Bashar al-Assad.
Syria’s authoritarian government favored Alawites and other minorities, widening social and political divides along sectarian lines. A sectarian civil war next door in Lebanon and the rise of Sunni religious politics widened them further, and Alawites continued to cluster in positions of power. The country’s Sunni Arab majority came to feel, at times, that they were underserved.
Minority governments like Syria’s tend to be unstable. They sometimes fear discrimination or worse should they lose power, and can see the majority group as a potential threat rather than a base of support. This can make them more willing to use violence to hold on to power — as Mr. Assad did when his forces opened fire on peaceful protesters in 2011.
As the war has worsened, many Syrians have based their allegiance on sectarian identity. But this is not because they are motived primarily by religious or ethnic concerns. Rather, it is defensive. They fear that the other side will target them for their background, so they feel safe only with their own people. This contributes to atrocities: If Alawites are seen as innately pro-Assad, then Sunni militias could conclude that all Alawite civilians are a threat and treat them accordingly, which prompts more defensive sorting.
At the same time, the Iran-Saudi Arabia proxy war is also playing out along sectarian lines, with the Saudis backing Sunnis and Iran backing Shiites across the region. For both countries, sectarianism is a tool by which they can cultivate proxy forces and stir up fear of the other side.
6. Where did the Islamic State come from?
The group has its roots in two earlier wars and the foreign occupations that followed: the 1979 Soviet invasion of Afghanistan and the American-led invasion of Iraq in 2003. In the first, Sunni Arab volunteers fought alongside Afghan rebels, later forming the global jihadist movement, including Al Qaeda. In the second, Al Qaeda and other Sunni groups flooded to Iraq to fight both the Americans and Iraq’s Shiite majority.
A key name is Abu Musab al-Zarqawi, a Jordanian extremist who fought in Afghanistan in the 1990s and Iraq in the 2000s. Mr. Zarqawi’s views and methods were even more extreme and theatrical than Al Qaeda’s. He flourished in Iraq’s war, using tactics now associated with the Islamic State: videotaped beheadings, mass killings of fellow Muslims deemed nonbelievers and attacks meant to incite a Sunni-Shiite war.
Al Qaeda invited Mr. Zarqawi to rebrand his group as Al Qaeda in Iraq, but the two factions argued over strategy and ideology, setting them up for conflict a decade later in Syria.
Mr. Zarqawi was killed in 2006, and his group declined as Sunni Iraqis turned against it. Later, Iraq’s Shiite-dominated government grew increasingly authoritarian and sectarian, alienating the minority Sunni. It also purged many experienced military and security officers, replacing them with political loyalists.
The successor to Mr. Zarqawi’s group, then calling itself the Islamic State in Iraq, exploited these conditions in 2011 and 2012 to reconstitute itself, for example by breaking extremists out of Iraqi prisons. Its leader, Abu Bakr al-Baghdadi, combined Mr. Zarqawi’s views with an apocalypticism taking hold amid the region’s upheaval.
Mr. Baghdadi sent a top officer into Syria’s war to set up a new Al Qaeda franchise: the Nusra Front, now known as the Levant Conquest Front. In 2013, Mr. Baghdadi declared himself commander of all Al Qaeda forces in Iraq and Syria. After years of tense partnership with Al Qaeda, the groups finally split. Mr. Baghdadi — his force now rebranded as the Islamic State — invaded Syria to fight his former Qaeda allies.
The Islamic State carved out a ministate in Syria’s chaos, then used it as a base to invade Iraq in 2014. It repeated Mr. Zarqawi’s worst tactics on a far larger scale, committing acts of genocide and mass murder in the Middle East and abroad, and attracting foreign recruits from rich and poor countries alike.
7. Why is the refugee crisis so severe?
The war in Syria has produced nearly five million refugees. The exodus has created three sets of problems, all dire: a humanitarian crisis for the refugees themselves, a potential crisis for the countries that host them and a political crisis in Europe over what to do.
Syrian refugees face disease and malnutrition. Host countries often bar them from working, meaning that families cannot provide for themselves. Many Syrian children are deprived of education, a problem that could hinder them for life.
Most Syrian refugees are in Jordan, Lebanon and Turkey, neighboring countries that lack the necessary resources to help them. The influx could be destabilizing, particularly in Jordan and Lebanon where Syrian refugees now make up a large share of the population.
Many refugees, unable to tolerate life in the camps, have braved the dangerous journey to Europe. But European voters have largely rejected them, supporting extreme measures to keep out Syrians and other migrants.
European leaders at one point suspended search-and-rescue missions in the Mediterranean, partly in response to complaints that saving refugees’ lives might encourage more to make the journey. Leaders of the campaign to get Britain to leave the European Union based their argument partly on opposition to accepting Syrian refugees.
Europe’s attitude appears driven by a combination of economic downturn; hostility toward the European Union, which allows unlimited migration among member states; and demographic anxiety rooted in longer-term trends that have made populations more diverse.
As a result, many refugees are stuck in camps in Italy and Greece. Many others die trying to reach Europe. European countries, along with the United States and Canada, have absorbed thousands of refugees, but not nearly enough to alter the underlying crisis.