The game's engine is inherited from the previous game. An interesting side effect of this is that you can now build buildings and defensive structures at the same time, which is insanly useful. Where, previously, the left side was for buildings and the right was for units, now each tab selects a different type of thing the player can build (buildings, defensive structures, infantry, and vehicles), and all those things the player can build under that heading appear in the two columns. The old two-column sidebar, staple of the series, is replaced by one with four tabs. Like any C&C game, RA2 isn't anything fundamentally new, but it is the biggest change yet in the C&C series. (Like the spy, the attack dog, the medic, the mobile gap generator, the radar jammer get the idea?) It was one of the first RTS's to offer a large number of specialized units. The single-player campaign featured some truly amazing scenarios (a level, for example, where you have to capture a building within a time limit, and then play another level inside the building with the time still running from the previous mission). The first Red Alert is one of the most innovative real-time strategy games ever made. This RTS, the sequel to Command & Conquer: Red Alert, was developed by Westwood Studios and published by Electronic Arts for the PC in 2000.