For much of the late 20th Century, a focus for many worldwide leftist movements was how unfair the world was. Determinism was in vogue, and a new rhetorical weapon was needed to show how horribly downtrodden the poor in the world were, and how they cannot help themselves.
(I shall let the reader ponder whether or not fostering this literally antisocial attitude of helplessness was itself a form of victimization.)
So the terms Global South and Global North came into being. Looking at a map of the world, one is struck my how much of the world's wealth is in the middle part of the Northern Hemisphere. The United States, the United Kingdom, France, Germany, and Japan share some latitudes. Back when people (especially the left) were impressed by the Soviet Union's performance, the correlation was even stronger. This is the core of the Global North
In the same way, a huge amount of misery (especially Africa) is in the southern half of the globe. This is the core of the Global South.
The other cause for the name was psychological. Most maps are oriented to Zero Degrees North. In this view, the north is "on top," and the south is "on bottom." This fits nicely with dependency theory, the belief that poor countries are always exploited in international trade. (Its relationship to Feminist Theory is also obvious.)
Like so much other clap-trap from the left, the name is garbage. Until her socialist government destroyed her economy, Argentina had an economy comparable to France. Australia (whose name means "South"!) and New Zealand are modern nations in the south*. South Africa is the richest and most powerful African nation. Under the leadership of Augusto Pinochet, Chile (whose contours plunge Southward) became the most successful South American nation.
But why let logic and facts get in the way of good ol' pseudogeography?
* but not of the South?