States sometimes go to war with former allies and sometimes make alliances with former enemies. Are there conditions which make wars between states less likely? Are there conditions which make alliances among states more likely?
When we think of war we are using an abstract concept to simplify our world as a kind of a lemma; of course, “the state” doesn’t reallye exist, but people do. What things make groups of people likelier to trust and trade? What things make groups of people likelier to fear, distrust, or even hate?
Abstractions of identity help to explain when groups are likelier to conflict or get along. Common points make conflicts less likely, and differences make conflict likelier. So the question of war in a sense is also the question of identity, of self as opposed to other.
What criteria do people use to identify themselves? Well, we are all human, so in principle we all could get along. Yet, even though we are all human some have different skin colors, others have different religious views, others have different languages, others still have different ideologies, different systems of government.
So, countries (abstractions from individuals) with common religions, languages, skin colors, and ideologies are likelier to get along as opposed to countries split by race, religion, language, and ideology.
Viewed in this light the USA and China may be doomed to conflict. Their ideologies and religions are quite different, so are their languages; and even race is to a larger extent than not different. All they really have in common is the desire to grow rich: they are culturally driven to acquire and enjoy property and to view property ownership as all important.
Viewed this way too the USA and Russia are likelier to get along than to conflict. Their religions are similar though not entirely the same; their racial composition is likewise similar, but not the same. Their contemporary ideologies are more similar than different. In short, the four splits, race, religion, ideology, and language are much less severe between the USA and Russia as compared to the USA and China or Russia and China. The Chinese-Russian relationship is thus more fragile, and the U.S. Russian conflicts are more illusory. It is likelier that the USA will be able to bring Russia into an anti-Chinese coalition than for China to bring Russia into an anti-USA coalition.