The Trump administration is hoping that its cruise missile strikes will solve a problem that has defied years of efforts: the willingness of the Syrian leader, Bashar al-Assad, to use chemical weapons.

But in a war with many dilemmas, this may be among the most intractable, analysts say.

It is driven by Mr. Assad’s own grim strategy and the limitations of American power, but also something deeper: the fundamental nature of the Syrian conflict and of chemical weaponry.

What follows are some of the forces prompting Mr. Assad to opt to use chemical weapons in Syria and why they are so resilient.

Syria’s Manpower Shortage

Mr. Assad relies on airstrikes, backed by allied Russian forces, which have helped him turn the war’s tide. But his greatest weakness is manpower: His ground forces, eroded by years of fighting, are simply too few to hold, much less advance, every front line.