The Underground Alliance was a militant group of armed civilians of Metropolitan City who were sided with the Alliance for the Survival of Humanity while being cut off from them by the League of Imperial Cybernetic Hybrids during the Battle for Metropolitan City. By the end of the battle, the group had evacuated the city & those who had remained were recruited into the Alliance, dissolving the entire force. The Underground Alliance, while only a small force meant mainly for Metropolitan City, later paved way for the rise of the Underground Resistance, which spanned across North America.
At some point after the Great Lakes Citadel's destruction & the beginning of the Battle for Metropolitan City, Luke & Maureen Anderson founded the Underground Alliance to protect the city from Imperials & shadowghosts who breached the security walls. The group, at first, was a small fraction of city civilians who were courageous enough to go into battle for self-defense. After the Alliance for the Survival of Humanity arrived in the city & the Imperials set up barriers, the group became every soldier caught outside Logan Square.
James Anderson arrived in Metropolitan some time after the Great Lakes Citadel collapsed. Upon arrival, he was arrested by Imperials & was going to be transformed into a hybrid. However, he escaped, made his way to Logan Square, where he found Eddie Smith & Emily Love waiting for him. They instructed him to go to his Metropolitan household, which was the headquarters for the Underground Alliance. When he arrived, the house was attacked by Blast Bots. After destroying the Blast Bots, James entered the Catacombs & destroyed the Mine Bridge operations being run by the shadowghosts & the Imperials. James then headed into the Catacombs once more to reach Logan Square. Later on, James returned after he raided the Imperial Fortress & found no way to return to the inside of Logan Square. Luke & James then led two divisions of the remaining Underground to attack the Imperials & shadowghosts from behind at their attack positions around Logan Square. By doing so, the Underground ultimately allowed the barriers to be shut down & destroyed & the Alliance trapped in the middle of Logan Square was able to exit the square through several corridors in all directions to access the rest of the city.
During James' time with the Underground Alliance, the Underground Alliance began to escort women, young children & others who were not able to defend themselves out of the city to the New Jersey countryside. From there, those escorted would take up home in the Anderson Manor before being relocated to New York II by either air train or ferry. Maureen Anderson, the co-founder, left the city just before James arrived, running the evacuation procedures from her side. After the entire barrier array around Logan Square was destroyed, the Underground Alliance soldiers joined up with the Alliance in the Square & anyone unwilling to fight alongside them left the city with Luke, who brought them to the Anderson Manor.
Civilians who were not soldiers of the Alliance that stayed behind during the final evacuations refused to surrender to Cyber Erol even after the Alliance relocated to New York II. Because of the readiness to destroy the Imperials, Erol dropped an atom bomb on Metropolitan, destroying the city & dissolving the Underground Alliance permanently.
The Underground Alliance, while a failure in the end, paved the way for the rise of the Underground Resistance, a fighting force of armed civilian militias that spanned from city to city across North America that even controlled minor settlements. The Resistance followed the practices of the Underground Alliance & even became a branch of the Alliance for the Survival of Humanity.