In 1901, San Andreas experienced a population boom of both immigrants and refugees, American businesses began investing heavily in the development of this tiny island nation off the Coast of Baja California, Mexico. On January 6th of 1912, when New Mexico was added as the 47th State, San Andreas as adopted as a territory of the United States.

After becoming a territory in 1912, the United State Government continued to send funds and materials to San Andreas to further modernize their infrastructure. In 1941, when Japan attacked Pearl Harbor, the San Andreas National Guard quickly mobilized and organized Relocation Centers for the Japanese Immigrants living on the island. In 1988, the San Andreas Government and United States Government formally apologized for the Centers and issued $20,000 to all survivors of the incident. Many San Andreans volunteered for service in the United States Armed Forces, seeing action in Pacific and European Theaters, there is a memorial garden located at City Hall in Los Santos. In 1946, after the war was officially over, the First high rise building was built in Los Santos and still stands today, the Los Santos Courthouse. In 1950, many San Andreans volunteered to join non combat units that were deployed to Korea. Many served as Doctors, Nurses, Medics, Drivers and Clerks.

The latter part of the 20th Century saw the mass introduction to automobiles and airports to the island. In 1964, the Los Santos International Airport, with support from the Los Angeles International Airport and FAA, was opened after a 5 year reclamation project was completed. It is the busiest Airport on the Island receiving over 100 flights daily. In 1965, the Police Action in Vietnam began and the United States Government asked the San Andreas Governor to start gathering volunteers, since San Andreas was not a state of the U.S.A. the draft could not be enforced. The Governor declined the requests stating, "The people of Vietnam are not our enemy, but we will continue to support the fight against Communism elsewhere." Many Americans agreed with this sediment, and supported the San Andreans for standing up for what they believed in. Many Government Officials openly accused the Government of San Andreas of either being "Commies" or too sympathetic toward the Vietnamese. As the Police Action in Vietnam was winding down the Governor of San Andreas offered assistance to the United States Government with the evacuation of their troops back home, which was accepted.

In recent years, San Andreas has partnered with Los Angeles and tourism has increased. Many that visit the island remark as to the similarities between Los Angeles and Los Santos. Since becoming a territory of the United States of America, the residents of San Andreas have enjoyed the Freedoms given to them by the United States and in 2021 was accepted into the Union as the 51st State.