Actually, Vietnam has been asserting its territorial rights in an increasingly sour dispute with China - but it's not reported on as much, because Vietnam is a smaller country. All sovereign countries are equal in some sense as being distinct entities whose existence is recognized by each other, which is a fine principle. but in terms of economic and military affairs size matters and thus the disposition of the largest countries captures most of the attention.

Think of the world like a zoo, all the different enclosures let you see a wide variety of animals. In nature, some of these animals share the ecosystem with each, others would never meet, such as kangaroos and camels. Now, if you opened all the enclosures and just let the animals go free inside the zoo, it's safe to predict that the elephants, rhinoceros, lions, and tigers will will shape things more (at the outset; over generations in a sufficiently large zoo results may vary) than coyotes, llamas, zebra, and camels. All the animals I've mentioned are optimized for different roles in different environments but some are better equipped to handle confrontation than others. I use the analogy of the zoo because it's small, like the planet as communications and transport technology have reduced epic journeys to a logistical operation. We're effectively walled in with much less psychic and transitional distance between us than there used to be.