In most types of strategy games, the player needs particular buildings in order to research specific technologies or build specific advanced units (StarCraft, Total Annihilation), while in other games upgrades/technologies are unlocked through research of their parent technology research (Warzone 2100). In many TBS games the prerequisite is one or more lower-level technologies, with no dependency on specific buildings (Master of Orion series, Civilization series, Space Empires series).[2][3][4] Most strategy games however use both systems. both requiring dedicated buildings and in advanced cases pre requisite technology, sometimes culminating in a game ending super-weapon of some kind.