When the U.S. becomes involved in Vietnam, the accepted wisdom in Washington is that "limited wars" are sometimes necessary, when the vital interests of the nation are at stake. In a sense, America's experience in Vietnam reaffirmed this viewpoint-but also revealed that in the future, the nation's interests would need to be of overwhelming significance.
In the decade after Vietnam, various administrations deployed armed forces on missions that the military was not equipped to fulfill. Multiple losses at the hands of terrorists (e.g., Iran and Lebanon) undermined the Pentagon's position when dealing with politicians.
During the Reagan years, the U.S. invested in a massive military build-up, a move toward the position of strength favored by Republican conservatives. In 1984, Secretary of Defense Caspar Weinberger outlined specific limits on the future use of combat forces. The six conditions required under the Weinberger Doctrine are as follows:
- The vital national interests of the U.S. (or close allies) must be at risk.
- War should be prosecuted "wholeheartedly, with the clear intention of winning."
- Decisive force should be employed in the pursuit of clearly defined political and military objectives.
- The use of force will be continually reassessed to determine whether it is still necessary and appropriate.
- There must be a "reasonable assurance" of Congressional and public support.
- Force should be used only as a last resort.
In reality, the guidelines of the doctrine are frequently bent to fit the needs of small-scale interventions. But all six conditions are met in 1990-91 during the Persian Gulf War. Of greatest importance to the military, the mission has a well-defined, achievable objective. The American victory supports the new thinking that decisive strength (rather than gradual escalation) might have improved the outcome in Vietnam.
Meanwhile, the collapse of the Soviet Union leaves the U.S. in a unique position as the world's only superpower. By 1993, Pres. George H. W. Bush relaxes the conditions of the Weinberger Doctrine, but supports the condition mandating a clear and achievable mission. The revised guidelines are sorely tested by crises in Somalia, Bosnia, and Haiti during the Clinton administration. In 1996, National Security Adviser Anthony Lake announces a set of circumstantial rules for applying force, guided by three principles:
- Credible threats can be as effective as force itself.
- Selective but substantial use of force is sometimes more appropriate than its massive use.
- Carefully defined exit strategies should accompany every foreign intervention.
In 2005, with an active war in Iraq, the effectiveness of these guidelines remains to be determined by future generations.