The original X-COM made its debut in 1994 and quickly cemented itself as one of the most influential tactical-strategy games of all time. The XCOM series has seen multiple installments since, culminating in 2012's reboot, XCOM: Enemy Unknown. Now, as we prepare to launch XCOM 2 this November, we look back on the last 21 years that lead up to this point in this IGN retrospective feature.