At the heart of President Obama’s threat to attack Syria for its alleged use of chemical weapons is a basic principle of international humanitarian law: the protection of innocent people from indiscriminate harm in warfare. Poisonous gases, by their nature, may float anywhere. They can wipe out entire neighborhoods – as the world saw in horrific videos from Syria last week.

The likely US weapon of choice in Syria – cruise missiles – can more precisely target ground objects than ever. The Pentagon has made great efforts to achieve “surgical” strikes of “strictly” military targets. And many experts predict Obama will choose the lowest-cost means of striking the armed forces of President Bashar al-Assad.

Nonetheless, such technology is war on the cheap. Soldiers on the ground are far more effective in avoiding civilian casualties. They might, for example, be better at detecting if Syrian forces have placed chemically loaded artillery shells or rockets near civilian areas. Close up, the lines of warfare are less blurry than from a satellite.

Yet troop warfare would come at a great price in lives and national treasure. The American people need to know if the cost of an attack on Syria is worth upholding an international principle of war.

The American commander in chief must be struggling to find a balance between such conflicting goals. How will Obama weigh efficiency and savings over strictly honoring humanitarian law? Or, to put it another way, will national interests override enforcing rules of war?

Humanitarian law recognizes war is never clean and easy. And the very idea of regulating behavior in war still seems absurd to many. Yet the world has become more sensitive to protecting innocent life in combat, especially with the American drone strikes in Pakistan and Yemen and with the US wars in Iraq and Afghanistan.

A similar outrage over collateral civilian damage occurred after the use of chemical weapons during World War I. That resulted in the 1925 Geneva Protocol, which outlawed such weapons – and today might provide legal justification for an international attack on Syria.

Obama needs to explain to Congress the difficult task of how he will protect Syria’s civilians from harm by US missile strikes. Also, he must explain how the United States will avoid the release of chemical weapons – especially mustard gas – in case such weapons are either targeted or inadvertently hit.

As much as the US military sees itself capable of avoiding civilian casualties, a perception persists worldwide that it can sometimes be careless. How many times have US commanders apologized for bombing errors in Afghanistan, Pakistan, and Iraq?

Making moral choices in war is a relatively new concept in the history of human warfare. One choice is preventing the victimization of innocent individuals, which would violate their right to life. War on the cheap should not be a war against this principle.