Third world nation doesn't cut it.Neither does developing or less developed,because the countries we use that label for have all had their natural resources developed right into the pockets of rich countries and companies.
Of course any term that aptly described those countries would not be very complimentary to us in the first or developed world.
Terms used now are more than a bit similar to the way we talk about rape, actually. First we talk around the acts of plunder and we never mention a perpetrator. When we talk about a woman being raped it's as if she was walking along and tripped and fell on an invisible, nameless, faceless thing called "rapist". When we talk about poor countries it's as if they are resource-free deserts and never acknowledge that their resources are stolen by the nameless, faceless thing called "capitalism".
I read once that the terms explorers used for newly discovered (by white people) lands were all feminine. "The lush, virgin forests need to be opened up for exploration" is the erotica of colonialism.
You can't fix a thing till you can properly name it. Rape doesn't end when we call it a "sex act", so what do we call this looting of poor countries?