2017. The original game, along with the expansion, was released for free in April 2017. Gameplay Blizzard Entertainment's use of three distinct races in StarCraft is widely credited with revolutionizing the real-time strategy genre. All units are unique to their respective races, and while rough comparisons can be drawn between certain types of units in the technology tree, every unit performs differently and requires different tactics for a player to succeed. The psionic and technologically adept Protoss have access to powerful units and machinery and advanced technologies such as energy shields and localized warp capabilities, powered by their psionic traits. However, their forces have lengthy and expensive manufacturing processes, encouraging players to follow a strategy of the quality of their units over the quantity. The insectoid Zerg possess entirely organic units and structures, which can be produced quickly and at a far cheaper cost to resources, but are accordingly weaker, relying on sheer numbers and speed to overwhelm enemies. The humanoid Terrans provide a middle ground between the other two races, providing units that are versatile and flexible. They have access to a range of more ballistic military technologies and machinery, such as tanks and nuclear weapons. Although each race is unique in its composition, no race has an innate advantage over the other. Each species is balanced out so that while they have different strengths, powers, and abilities, their overall strength is the same. StarCraft features artificial intelligence that scales in difficulty, although the player cannot change the difficulty level in the single-player campaigns. Each campaign starts with enemy factions running easy AI modes, scaling through the course of the campaign to the hardest AI modes. In the level editor provided with the game, a designer has access to four levels of AI difficulties: "easy", "medium", "hard", and "insane", each setting differing in the units and technologies allowed to an AI faction and the extent of the AI's tactical and strategic planning. The single-player campaign consists of thirty missions, split into ten for each race. Resource management Each race relies on two resources to sustain their game economies and to build their forces: minerals and vespene gas. Minerals are needed for all units and structures, and they are obtained by using a worker unit to harvest the resource directly from mineral nodes scattered around the battlefield. Players require vespene gas to construct advanced units and buildings, and they acquire