As others allude to, natural resources are zero sum, they are a finite resource, once they are gone, they are gone.
So if an imperial power is mining resources from a 'colony', that 'colony' is being stripped of economic potential with very little to show for it.
They do not both gain economically, like some allude to when maybe it is two countries sharing manufactured goods.
Edit: as an exercise, consider the land value of a typical office, and compare to the annual income of the part of the company based there, and the personal income of the employees who work there.
Most parts of the global economy are. If you're selling cars for example, there's a fixed amount of drivers on the road you can sell cars to, so if you're VW, you're now competing with cheaper cars from Asia for those same drivers.
You can't create new drivers out of thin air to expand the market demand for cars. Once the market is saturated, without having any moat, you enter in a race to the bottom.
And that's what Germany's economy is discovering right now and why Europe's share of global GDP has been declining for the past 20 years.
Also, we shouldn't care about Europe's share of global GDP. We should care about how the poor people in our countries are doing. Like I said, we should maintain or improve our quality of life. Producing cars is just a means to an end.