Dependency theorists explain global inequality and global stratification by focusing on the way that:
core nations and peripheral nations exploit semi-peripheral nations
semi-peripheral nations exploit core nations
peripheral nations exploit core nations
core nations exploit peripheral nations

core nations exploit peripheral nations

Explanation:

Immanuel Wallerstein is one of the dependency theorists  that explains global inequality in the international system, According to his neo marxist theory:

Global stratification occurs as core nations exploit the peripheral nations that basically are producers of raw materials and generate cheap labor force.

The dependency theory suggests that the current capitalist system perpetuates inequalities since it reproduces conditions where global markets are controlled by nations like England or the US that are at the core, while other states are semi peripheral and serve as a bridge.

In other words: Dependency theory states that as long as peripheral nations keep relying on core nations for economic stimulus and access to a larger piece of the global economy, they will never gain the stable and consistent economic growth promised.