Unfortunately colonizers carving the continent up during the last couple centuries into "countries" with little regard to existing ethnic, cultural, and political dynamics has only blown this up. Hard existing in a peaceful equilibrium if a border now splits your ethnic group in half and includes some part of some other group, all now supposed to be governed under the same political entity. And also having to start with ravaged economic and social infrastructure.
America has more diverse and more ethnic groups and we are excepted to get along.
National borders everywhere have little to do with historical ethnic and cultural groups. It's tough but that's just how it is everywhere.