In Pilot, Part 2, Sayid reveals to Hurley that he was a military communications officer who saw battle during the Gulf War:
SAYID: I was a military communications officer.
HURLEY: Oh yeah? You ever see battle?
SAYID: I fought in the Gulf War.
HURLEY: No way! I got a buddy who fought over there. He was in the 104th airborne. What were you - Air Force... Army?
SAYID: The Republican Guard.
[Sayid starts with the bamboo under the fingernails.]
SAWYER: That's it? That's all you got? Splinters? No wonder we kicked your ass in the Gulf. . . [he screams].
In Outlaws, Hurley asks Sayid if he ever suffered from Gulf War Syndrome, which Sayid notes was on the "other" side.
In One of Them, Sayid and his commanding officer are caught by the Americans during the Gulf War.
The Gulf War or the Persian Gulf War (2 August
1990–28 February 1991)was a conflict between Iraq and a coalition
force of approximately 30 nations led and authorized by the United
Nations (UN) in order to liberate Kuwait.
The war developed out of the Iraqi invasion of Kuwait on August 2,
1990. The aggression was met with immediate economic sanctions by the
UN against Iraq. The international armed intervention began in January
1991 and resulted in a decisive victory for the coalition forces, which
drove Iraqi forces out of Kuwait with minimal coalition deaths. Aerial
and ground combat was confined to Iraq, Kuwait, and bordering areas of
Saudi Arabia. Iraq also launched missiles against targets in Saudi
Arabia and Israel.
Since the Iran-Iraq War of 1980-88 had been called the "Gulf War"
or "Persian Gulf War" by many news sources, the 1991 war has sometimes
been called the Second Gulf War, but more commonly, the 1991 war is
styled simply the "(Persian) Gulf War" or the "First Gulf War", in
distinction from the 2003 Invasion of Iraq. Operation Desert Storm was
the U.S. name of the air and land operations and is often used to refer
to the conflict. 
