Capitalism is absurdly inneficient for maintaining long term humanity interests, e.g. the U.S became a third world country since they let westinghouse dies in darkness. https://www.nytimes.com/2017/03/29/business/westinghouse-tos...
The second world is USSR and associated allies.
The third world is everyone else. Implying they are too insignificant to be allied to either. Which isn't necessarily the case. Finland and Sweden are technically "third world" countries, as they are not NATO members.