Many different groups helped in the building of the Korean Wall.
The correct answer is - trade.
The Sumerians engaged in trade with their move of exchanging their surplus food for materials like the copper that they needed to develop their weapons and thus their army forces. This was a very smart move from their side because they managed to use the resource they had in abundance but was scarce in the other surrounding areas so that they take what they need to become stronger and pretty much defend more efficiently from the same people they were engaging in trade with.
A violent Civil war in Colombia that has lasted over 30 years is being financed by Communist Cuba.
