As the debate over military action in Syria has unfolded in the West, Iraq’s own painful history with American military intervention, and the false intelligence put forward to justify it, has provided a counternarrative to those who support intervention. Haunted by the intelligence failures, the British Parliament voted against strikes on Syria.

For the same reason, the American public, polls show, is also hesitant to back a new military strike in the Middle East.

For Iraqis, the fate of the two countries is seen as inextricably intertwined, and thus they believe they have a great deal at stake in what decision is made in Washington. The war in Iraq has already inflamed sectarian tensions, emboldening Sunni extremists to raise the tempo of attacks against the Shiite-dominated government, while also motivating Shiite men, with support from Iran, to travel to Syria to fight alongside the government forces and their ally, the Lebanese Shiite group Hezbollah.

“America wants to help the extremists to control Syria, but they are wrong because we will defend our sect,” said Abu Mohaned, who vowed that any American military action would inspire Iraqi Shiites to send fighters and weapons into Syria. “They will commit a big mistake if they think it will be easy to strike Syria and change everything. We all have faith that God is on our side, and we will show them that the Shiites in all the world are able to fight their proxies from Al Qaeda and Nusra and the hated Free Syrian Army.”

Iran has sent members of its paramilitary Quds Force to Syria, and Qassim Suleimani, the force’s commander, who has orchestrated the Shiite violence in Iraq from Tehran and expanded Iran’s role in Baghdad, has provided military aid for Mr. Assad, according to American officials.