What does it do to you to pass a drowning person without reaching out to help? Worse yet, what does it do to you to exploit them as they drown? What does it mean for you for that course of action to even be possible given your constitution?
In the times I've seen the drowning person thought experiment come up in ethics, it has usually been individualized, a common enough occurrence. But it can very easily be applied to the rhythmic rise and fall of empires given the dynamics involved in that process.
It was the troubled lands of the decaying Songhai empire and beyond that served as virtual quarries for slave labor, indulging the voracious European demand for exploited labor in the plantations of the New World. Even the more thoughtful of the colonizers themselves would warily view the huge transplanted populations of slave labor in their growing societies as potentially explosive elements that could seriously complicate domestic social problems or even detonate them. And of course from our historical vantage point, we could see that that was a wound that never closed, and which indeed widens alongside many others as the Western world advances into its own cycle of decay.
Consider also the Ottoman Middle East, which weakened at the joints after the first World War, was finally dismembered and partitioned out by the victorious powers, an exploitative relationship and process that would have profound effects on modern world history.
In so many words, the sites of decaying fallen empires make for dangerous and lucrative sites of prolific resource. There are no longer stronger unified powers present to defend their interests, and the fragments can be turned against each other and manipulated to facilitate the plunder, but at the same time the turbulent forces present within dissolution are still there, still well able to influence any power that participates in it.
That is part of the reason these sites of exploitation become both resource quarries and traps, depending on the interest involved. In countless Great Game dynamics across history, one empire would go into their preferred stomping ground of plunder while a rival would manipulate the region from the sidelines in hopes of snagging their foe in resource sinks and bad politics.
During the first Cold War between the USSR and the US for example, the regions of the developing world would serve as both sites of intense exploitation and entrapment, with the US manipulating and grooming the regions for plunder and the USSR sending in arms and resources to strengthen their chosen allies and to stymie the US' efforts, and vice versa, the roles changing depending on who controlled a given region.
This works because the control of a given region of exploitation requires resources and efforts in itself, which is worthwhile to the colonizer so long as the net return on investment is substantial enough. But what happens throughout history is that sustained colonial exploitation causes progressively more chaos - both within the colonies and within the colonizing powers themselves - and a declining rate of return, a dynamic that is difficult to escape for a proud imperial power refusing to walk away from its historical commitments.
The centuries old struggle over the Middle East is a case in point. The region has a long history of outside interference, much of it lying right in the middle of important overland trade routes between the East and West, but to make a tidier point, it was not long ago that the Soviet Union was rolling through Afghanistan and getting bogged down fighting the US-backed Mujahedeen, and then not long after that, the United States would do the invading and bogging down in the region, though at this time the USSR had collapsed and Russia was a shadow of its former self.
To address more modern forms of colonialism and imperialism, counterinsurgency is a nasty business. To be successful in it you have to regularly carry out atrocities over a longer period of time; it is an asymmetrical war of attrition. This procession of atrocities creates more and more enemies and provides grist for oppositional propaganda, and it provides domestic categories for enemies at home. It induces a military buildup which puts a drain on resources, and it engenders a political paranoia - encouraged by increasing anger abroad and at home - that encourages further militarization and the development of police states, destroying trust, requiring further costly militarization, and so on.
Getting bogged down in foreign wars is deleterious for even strong and vibrant empires, and it can be deadly for weak ones, which is part of the reason why these sites of exploitation and insurgency tend to grow and fester beyond the already grim facts of continued exploitation itself. Outside rival powers are all too happy to leverage the corrupting forces of colonization.
