Variants of realism argue that the environment among countries is very much a Darwinian struggle of survival of the fittest. Those countries that fail to compete are eliminated from the system or, at the very least, are made irrelevant and subservient. The problem is that the folks making such arguments either haven't had small children or did not watch TV with them.
When my daughter was younger, she watched a heap of Animal Planet shows, and the thing one quickly realizes is that even in a harsh world where there are predators everywhere (some folks in IR question whether predators need to exist in order for anarchy to be so nasty and for security dilemmas to develop), there are a myriad of strategies and endowments that allow heaps of different species to survive and thrive, if not dominate.
- Speed can be handy (Cheetahs)
- You can be slow if you have a shell (turtles, snails).
- You can be poisonous (heaps of spiders, snakes, etc).
- You can just appear to be poisonous (red frogs).
In the 1980's, there was much debate about who adjusted well to the international economic shocks of the 1970's, especially higher oil prices (Between Power and Plenty). The new conventional wisdom was that governments that could best resist societal pressures (France, Japan) adapted better than those that cannot (US). However, over time, it become clear that the US strategy of letting the market force much of the adaptation was not a bad way to go (Irony of State Strength). The point is that there are a variety of tradeoffs that outside pressures may impose, but how one manages those tradeoffs will vary.
We need other elements to produce predictions and explanations for the choices countries make, since there is more than one way to skin a cat or to survive in the international system. I am not the first IR scholar to say that Realism is indeterminate. I am just the first one to invoke Animal Planet to make that point.