Systems Alliance Colonial Army (SACA)
Active:	14 January 2158 CE - 7 June 2186 CE 1 October 2186 CE - 31 December 2191 CE
Organization:	Systems Alliance Armed Forces
Affiliation:	Systems Alliance
Type:	Volunteer civilian militia
Role:	Colonial defense Tactical law enforcement
Size:	4 million 1,500 aircraft
Part of:	Systems Alliance Joint-Colonial Command
Headquarters:	New Xi'an, Shanxi
Motto:	"Immovable." (English translation)
Colors:	Navy blue and black
Engagements:	First Contact War Skyllian Blitz Reaper War
Commanders:	Gen. Autumn Santana (last)

"Res immobiles."

— SACA motto.

The Systems Alliance Colonial Army (SACA), also referred to as the Alliance Guard and Alliance Colonial Guard, and as the Human Guard and Human Home Forces to aliens, was the armed citizen militia and home land defense branch of the Systems Alliance Armed Forces, and one of the four uniformed services of the Systems Alliance. The origins of the Colonial Army date back to the formation of the Shanxi Colonial Guard on 10 July 2153 CE, which was originally formed as an armed civilian militia separate from the Alliance, made up of volunteers who were paranoid of alien invasion and wished to have a means to defend themselves for if an attack came, not wanting to rely on the Alliance Army. The Shanxi Colonial Guard put up a fierce struggle during the First Battle of Shanxi, waged a small guerilla campaign during the planet's occupation, and provided internal aid to Alliance forces liberating the planet. After the First Contact War, the Shanxi Colonial Guard proved itself so effective that the Alliance made plans to introduce them as the fourth and final branch of the military, separate from the Army with a focus on defending Shanxi: while the branch would remain as an armed civilian militia consisting only of volunteers, they would be given Alliance training, access to military-grade weaponry and equipment, and would answer to Alliance brass, with their own dedicated subcommand. In mid 2158 CE, armed militias that had formed on Terra Nova and Elysium were also incorporated into the branch, being combined with the Shanxi Colonial Guard to become the first three guard armies of the Colonial Army, with the branch adopting the name fully in 2159 CE. The Colonial Army continued to grow in the years following as more armed militias were introduced to most of humanity's primary colonies, with smaller guard units later established on developing colonies after the Sack of Mindoir in 2170 CE.

The Colonial Army was the only branch of the Alliance military with a purely defensive purpose, with no offensive capabilities whatsoever. In peacetime, the Colonial Army provided law and order to their respective colonies, and in terms of civil strife or unrest, they could be deployed at a moment's notice to restore order, and in escalating situations that local law enforcement couldn't handle, the Colonial Army would be called in to provide assistance. In wartime, the Colonial Army would supplement Alliance ground forces in the defense of human colonies, or to substitute them, freeing up Army and Marine Corps resources for offensive operations elsewhere. The Colonial Army's unique status as a volunteer militia filled with armed citizens gave it access to manpower at a moment's notice that the Army couldn't necessarily provide, with the majority of a Colonial Guard unit at any given time being inactive, with only a small percentage of it active, with the rest of it being quickly mobilized when needed. During the Reaper War, the Colonial Army suffered heavy losses during the early stages of the Reaper invasion, with many colonial guard units being wiped out as they defended their homes. From the 5 June onwards, the Colonial Army was deactivated, with its surviving members being reassigned to the Army and Marine Corps, while those who had failed to escape their colonies joined local resistance groups, making use of their Alliance training to quickly rally men and women of fighting age to resist Reaper occupations across conquered Alliance territory. After the Reaper War ended, the Colonial Army was reactivated, and the members who survived were reassigned to the branch shortly thereafter. With the dissolution of the Alliance in 2191 CE, the Colonial Army was reorganized into the Systems Coalition Colonial Guard.