Just a quibble, but it is not necessarily "countries" that represent "tribes" or, more accurately "cultures". There are many countries with more than one culture included inside their controlled territories - which often leads to conflicts within countries. And there are some cultures that have no territory that they control - leading to conflicts within the countries where they live.
It is mainly about various cultures fighting over resources. And, it is not necessarily about just ensuring that there is "enough" for a culture's population to survive or even thrive. The competition created conflicts have been going on for so long that they are built into our cultures and probably even our DNA to want control, not just trust, that they will survive and thrive.
I wonder how far back in the evolution of the human species that paradigm originated. Other social species also have intra-population "wars" when they start to exceed the resources in their territories. Even a successful wolf pack, when it grows too large, splits into 2 packs and those 2 packs often become deadly enemies, unless they can separate sufficiently to have distinct territories that do not overlap.
Looking at what has driven our species technological development, it seems that has mostly resulted from intra-species conflicts for resources as our population has expanded in various places at various times.
If we all just got along, with plenty of resources to satisfy everybody, would we really have expended the effort to go to the Moon and beyond? Or, would we be more like our evolutionary cousins, the gorillas?
And, what should we really expect from some extraterrestrial species that has been motivated to get to Earth from wherever? How confident can we be that they are driven only by benign scientific curiosity, rather than a need for more resources? Would they really sit back and watch? Or, would they colonize Earth when they get here?