The 9th Division was activated as a peacetime readiness unit from 1947 to 1962 at Fort Dix, New Jersey and Fort Carson, Colorado, and from 1972 to 1991 as an active-duty infantry division at Fort Lewis, Washington. During Vietnam War the division participated in Operation Speedy Express.

Following the Vietnam War the division was stationed at Fort Lewis Washington until its inactivation in 1992. Beginning in the mid-1980s the division served as the high-technology test-bed for the army. This led to the division testing the concept of "motorized infantry," designed to fill the gap between light infantry and heavy mechanized forces. The idea was to create lighter, mobile units capable of rapid deployment with far less aircraft than a heavier mechanized unit. Motorized infantry doctrine concentrated on effectiveness in desert warfare.

By 1989 the division had fielded two complete brigades of motorized infantry in battalions designated as either "Motorized" or "Attack." Motorized battalions traveled in the new High Mobility Multipurpose Wheeled Vehicle (HMMWV) and generally fought as traditional light infantry once engaged. Attack battalions utilized the Fast Attack Vehicles (later re-designated the Desert Patrol Vehicle), first developed at Fort Lewis. Essentially a Volkswagen- engined dune buggy mounted with either a 40mm Mk 19 grenade launcher or .50 caliber M2 Browning machine gun, the FAV was designed to provide highly mobile firepower that could attack the flanks of heavier mechanized units. Some variants also mounted TOW missiles. All of these weapons systems were attached to the FAV by a mount designed to break away if the vehicle rolled over, which they were prone to do. The FAVs were problematic at best and were eventually replaced by various versions of the HMMWV.

The 9th Infantry Division (MTZ) tested motorized infantry doctrine at the Yakima Firing Center in Eastern Washington, at the National Training Center at Fort Irwin California and in Korea during the annual Team Spirit exercise. While the motorized units performed well they were vulnerable to heavier mechanized forces, particularly if forced to stand and fight. They were also extremely vulnerable to indirect (artillery) fires.
At the end of the Cold War the division was identified for inactivation. By the time of the First Gulf War one brigade was nearly inactivated. However the 3rd Brigade was still at full strength. The need for mobile forces that could be more easily deployed would seem to have never been greater. However the brigade was not deployed to the Middle East, instead providing soldiers and equipment to fill out deploying units from other divisions. While the rest of the army went to war, the 9th ID focused on inactivation and training National Guard and Army Reserve units deploying to the Persian Gulf.

Inactivation
The division was the first to undergo full deactivation following the end of the Cold War. Army leadership at first decided that deactivating units would turn in all of their equipment at "10/20" standard - in ready and reusable condition. The division struggled to meet this standard. It required both unrealistic work on the part of the division's soldiers and very high costs in repair parts. While the remaining 9th ID soldiers were ultimately successful, later deactivating units were not required to attain this difficult goal.
The existing 3rd Brigade did not deactivate and was instead re-designated the 199th Light Infantry Brigade and assigned directly to I Corps. The 199th was later re-designated the 2nd Armored Cavalry Regiment (Light) and was transferred to Fort Polk, Louisiana.
By December 1991 the final units of the 9th Infantry Division had cased its colors, ending over 50 years of valorous service.