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.

Image: 25 March 2015: A Kurdish Syrian woman walks with her child past the ruins of the town of KobaneYasin Akgul/AFP.