That's racist!

[Abacab "The REAL truth"]

To make it easier for you:

There are two tribes, one to the far north and one to the far south, the north tribe lives in a rocky forested region rich with minerals, lumber, and fairer weather. The group to the south lives in a desert basin.

The south tribe living in an area with such a disadvantage has to eek out what shelter and protection they can, so they're building houses out of reeds, sticks, mud and rock, as this is their only resource in the area. They easily thrive because they build near rivers so they have irrigation systems and clean water at all times.

The tribe to the north has the benefit of living in a secluded area, building houses out of stone, hard lumber, and animal pelt. They thrive due to the variety of their area, hunting game, foraging, making elaborate weapons and traps for the purpose of killing animals.

These two tribes eventually clash over a middle region, the southern tribe who has mostly been a fishing/agricultural society loses in combat to the northern tribe because the northern tribe has perfected stone weaponry, projectiles, and is more adapted to surviving on the go than the southern tribe who has simply settled into a river.

The southern tribe goes back with the loss but they learn how to make stone weaponry and now use that knowledge to change their society based on the northern tribes advancements so next they clash they are on equal footing.

The northern tribe sees this as an issue, so they use harder substances for weaponry leaving behind stone and bone they begin to dig deeper finding harder stones and finally copper, they melt this copper down and pound it out to have a sharp edge which has the ability to cut through stick, stone, and bone. With that advancement they're able to push the south back again because the southern tribe cannot compete with this advancement and even worse the southern tribe doesn't have any form of copper to match par.

The northern tribe begins to fight within itself, moving from copper to iron, from iron to steel just to fight for dominance because the northern tribe has the advantage of resource they out-progress the southern tribe entirely as they're still stick and stone and now the northern tribes are competing with other northern tribes to which each side makes an advancement which is then emulated and improved upon.