Concept
Civilization (series)
Related concepts (13)
Technology tree
[[File:Freeciv-2.1.8 technology tree (cropped).png|thumb|upright=1.5|Part of Freecivs technology tree, showing complex dependencies between technologies. For example, astronomy can be reached by first researching ceremonial burial and then mysticism, or by researching masonry followed by mathematics]] In strategy games, a technology, tech, or research tree is a hierarchical visual representation of the possible sequences of upgrades a player can unlock (most typically representing the research progress of a given faction).
4X
4X (abbreviation of Explore, Expand, Exploit, Exterminate) is a subgenre of strategy-based computer and board games, and includes both turn-based and real-time strategy titles. The gameplay generally involves building an empire. Emphasis is placed upon economic and technological development, as well as a range of military and non-military routes to supremacy. The earliest 4X games borrowed ideas from board games and 1970s text-based computer games. The first 4X computer games were turn-based, but real-time 4X games are common.
XCOM
XCOM (originally called X-COM) is a science fiction video game franchise featuring an elite international organization tasked with countering alien invasions of Earth. The series began with the strategy video game X-COM: UFO Defense created by Julian Gollop's Mythos Games and MicroProse in 1994. The original lineup by MicroProse included six published and at least two canceled games, as well as two novels.