video games in that the player must manage units with a variety of numeric attributes, RPGs tend to be about a smaller number of unique characters, while strategy games focus on larger numbers of fairly similar units. Game design Units and conflict The player commands their forces by selecting a unit, usually by clicking it with the mouse, and issuing an order from a menu. Keyboard shortcuts become important for advanced players, as speed is often an important factor. Units can typically move, attack, stop, hold a position, although other strategy games offer more complex orders. Units may even have specialized abilities, such as the ability to become invisible to other units, usually balanced with abilities that detect otherwise invisible things. Some strategy games even offer special leader units that provide a bonus to other units. Units may also have the ability to sail or fly over otherwise impassable terrain, or provide transport for other units. Non-combat abilities often include the ability to repair or construct other units or buildings. Even in imaginary or fantastic conflicts, strategy games try to reproduce important tactical situations throughout history. Techniques such as flanking, making diversions, or cutting supply lines may become integral parts of managing combat. Terrain becomes an important part of strategy, since units may gain or lose advantages based on the landscape. Some strategy games such as Civilization III and Medieval 2: Total War involve other forms of conflict such as diplomacy and espionage. However, warfare is the most common form of conflict, as game designers have found it difficult to make non-violent forms of conflict as appealing. Economy, resources and upgrades Strategy games often involve other economic challenges. These can include building construction, population maintenance, and resource management. Strategy games frequently make use of a windowed interface to manage these complex challenges. Most strategy games allow players to accumulate resources which can be converted to units, or converted to buildings such as factories that produce more units. The quantity and types of resources vary from game to game. Some games will emphasize resource acquisition by scattering large quantities throughout the map, while other games will put more emphasis on how resources are managed and applied by balancing the availability of resources between players. To a lesser extent, some strategy games give players a fixed quantity of units at the start of the game. Strategy games often allow the player to