She then moved to the Center for Strategic and International Studies (CSIS), where she worked as a senior advisor on a range of defense policy and international security issues. In 2002, a year before the US invasion of Iraq, she argued for preemptive strikes by the US against foreign weapons stockpiles. Flournoy told "The Washington Post", "In some cases, preemptive strikes against an adversary's [weapons of mass destruction] capabilities may be the best or only option we have to avert a catastrophic attack against the United States."