During the age of conquest Spain was able to extract natural resources (such as minerals), but for the most part, Britain, Portugal, France benefitted from the trade with their colonists --not trade with new world peoples.
I think it could be argued that this reliance on natural resources by Spain, contrasted with commerce favored by Britain, for example, resulted in the slow decline of imperial power by Spain. I think by the 1800s, Spain had pretty much ceased to be economically relevant vis-a-vis the more commerce oriented Empires of the time.
A crude analogy would be China selling to their diaspora outside China proper.
There isn't much of a distinction between exploiting natural resources and settling colonists so the colonists could exploit natural resources for you. The colonial American south exported tobacco and cotton, for instance.
The UK extracted immense amounts of wealth from India alone - where is China's India? Africa was plundered in all senses of the word by western Europe. It's not just Spanish gold that I'm referring to.
My point is that the strength of the UK economy of the time wasn't just 'factory workers', conquering a quarter of the world's landmass and nicking their stuff also helped significantly. China can't replicate this.
The question is whether it's more productive to conquer other continents and plunder them with 18th century technology or just produce stuff with 21st century technology. And it's not as easy as you'd think. Most of the imperial powers spent a lot of money on things like shipping people across oceans, maintaining vast military forces to guard their empires, building massive amounts of infrastructure in their empires, trying to convert the natives to Christianity or at least stop them from immolating themselves on their husbands' funeral pyres, teaching the natives to govern themselves, getting into wars with your colonists when they want to be an independent country, and getting into wars with the natives when they want to be an independent country. Adding insult to injury, having huge empires means a war with the neighboring European country turns into a huge world war between your colonies and the enemy's colonies. It gets so expensive that eventually you have to abandon your colonies--and it's not like India or Africa just ran out of natural resources. Quite the opposite, really.
So instead of messing around with all of that, China's expenses are limited to building infrastructure in China, maintaining vast military forces to guard China and occasionally menace Taiwan, and converting the Chinese to some vaguely secular state-approved worldview. And they have the benefit of modern technology and the entire developed world to crib notes from. They don't have to figure this shit out the first time. A factory anywhere in the West in the 19th century was a best guess--a Chinese factory today benefits from 200 years of experience and empirical research into how to run a factory, robots, computers, a huge foreign population of people buying stuff, and thousands of Western-educated professionals. I think China has the advantage.
China has plenty of shit to figure out for the first time - things like the one-child policy are evidence of this. But my real issue is that the idea that western europe industrialised and became an economic powerhouse just on the basis of it's own factory sweat is a poor reading of history.
Also, not sure what you mean by world war between colonies. Spain, England and France had numerous colonies, but didn't abandon them when warring between each other. Germany, Austro-Hungary and Italy weren't big on colonies, and neither World War involved much in the way of colony-on-colony fighting - pretty much all things you would call a colony in some way were fighting on the side of the Allies in both wars.
There were probably a half dozen wars before World War I that involved colonial theatres. The Dutch-Portuguese war, the Seven Years' War, the War of Austrian Succession, and the War of Spanish Succession are some examples. Many of these are considered world wars for that very reason.
Oh yeah--France actually did abandon their American colonies during the Napoleonic Wars. Haiti had a revolution and Napoleon needed money to try and conquer Europe, so he sold Louisiana to the United States.
I think it could be argued that this reliance on natural resources by Spain, contrasted with commerce favored by Britain, for example, resulted in the slow decline of imperial power by Spain. I think by the 1800s, Spain had pretty much ceased to be economically relevant vis-a-vis the more commerce oriented Empires of the time.
A crude analogy would be China selling to their diaspora outside China proper.