The first game in the series was originally released in Japan as "Simple 2000 Vol. 31: The 地球防衛軍" for the Playstation 2. "Chikyū Bōeigun" or "Earth Defense Force" was created by Sandlot Games as part of D3 Publisher's Simple Series of budget-priced games on compact disk. It was later distributed in PAL format on CD in Europe by Agetec, Inc. under the title "Monster Attack". Source: Wikipedia, "Earth Defense Force (series)", available under the CC-BY-SA License.