Wheat.

This is coolbert:

Wage war by hunger. Break the will of the adversary to continue the fight by depriving them of food!

As has been the case in Syria. Assad using food as a weapon.

"The most unconventional weapon in Syria: Wheat"

As originally from WaPo [Washington Post] thanks in this case to Freeper:

"In the fall of 2012, fighters from the Free Syrian Army [FSA] took over Eastern Ghouta, a semi-agricultural area about eight miles northeast of Damascus. Government forces responded by placing the area under siege, cutting off water, electricity, gas, medical assistance and bread."

"The regime's goal was to starve the people of Eastern Ghouta into submission, and it was working: The price of bread and rice went up 50 times. Locals were living on animal feed or sometimes eating nothing at all."

"Nine months later, the Free Syrian Army [FSA] mounted a military operation in a regime-controlled area called al-Matahin, the Mills, just outside Eastern Ghouta. Its objective was a flour mill, flanked by two rows of grain silos that housed part of the Syrian government's strategic wheat reserves . . .  If the opposition could capture the mill, it could keep the wheat, break the siege, gain a strategic point on the airport road, and perhaps even make some money."

"The firefight lasted a day and a half. Before the battle ended on the second day, anti-government fighters sent a message via walkie-talkie to aid workers waiting inside Eastern Ghouta: 'We are in partial control of the mill. Come and help us get the flour'."

The Islamic State perhaps their most valuable asset the cropland they control. A cash asset those crops sold and taxes as derived from sale of same also a tool by which to exercise control over the populace. 

"IF YOU ARE WITH US YOU EAT! IF YOU ARE AGAINST US YOU STARVE!"

That ruthlessness of ISIL undeniable!

P.S.: See the American Operation Starvation from the era of the Second World War [WW2]. If the war in the Pacific had become a protracted affair from 1945 onward as many as 10 million Japanese might have died of starvation of complications arising from the lack of food!!

coolbert.