A revolution is when a country has chosen to unlock specific technologies, while keeping others locked. A country can choose only one revolution, and if it is unsatisfied with the revolution it has chosen, it can change the revolution for a fee, with the exception of the Space revolution. There are currently 5 types of revolutions.
Industrial revolution is a revolution which specializes in using resources. Countries with industrial revolution can use up (remove) a resource for temporary bonuses, try to find resources for a cost, and even shape their landscape (change land, mountains and water). This revolution is balanced, but requires a tactical approach. In war, it uses various materials to build tanks and modifying landscape, while in peace it still modifies the landscape and manages resources.
Corporate revolution is a revolution which specializes in spending and earning GC. Countries with corporate revolution can create companies, buy mercenaries and even buy tiles from other nations. They can even bribe other soldiers to fight for them. This revolution is specialized in funding and diplomacy, for example, using corporations to earn more GC. Although it is not a combat-based revolution, it can wage war indirectly, using mercenaries (unknown nation) and the Riotmaker to attack rival nations.
Atomic revolution is a revolution which specializes in nuclear warfare and military. Countries with atomic revolution can create nukes, create more military (+1 division for each ruined city) and even make uninhabitable tiles habitable. This revolution is combat-based, being able to build nuke shelters, inhabit uninhabitable tiles and even build the Nuke superweapon. However, during peacetime it can construct useful, but deadly nuclear power generators.
Polar revolution is a revolution which specializes in colonizing the ice caps of Ukiworld. Countries with polar revolution can create polar colonies, polar laboratories and military bases, harness the polar resources and even populate ice and tundra tiles. This revolution is specialized in peaceful colonization, often needing allies in case it gets attacked. However, the its colonies require less protection because of the major debuffs enemy soldiers face while on ice.
Space revolution is the final revolution, which specializes in colonizing planets. Unlike other revolutions, space revolution has a little bit of other revolution's techs, like polar colonies and using up resources. It enables the nation to research space techs, such as the Space Life Test and the VATROS. Entering the space revolution marks the beginning of space age.