Fault line conflicts
Fault line conflicts were first defined, by by Samuel Huntington in The Clash of Civilizations and the Remaking of World Order, as clashes between civilizations within one physical cleft country. His first example was the former Yugoslavia, where Serbs from the Slavic civilization clashed with other peoples from Muslim civilization. Lebanon has its Western Christian vs. Muslim clash.
The term still has value if a broader definition of "civilization" is used, so that it considers major ethnic, religious, or tribal groupings within a nation. Iraq is one such case where the fault lines create Islamic sectarian conflict.
There are many cases, such as Rwanda, where colonial map-drawing threw different groups into a pseudo-nation. Even harder to characterize are cases such as Afghanistan, Pakistan and India, where the Durand Line separated the Pashtun people, or where the Kurds are separated by the states of Turkey, Iran and Iraq.