Civil war
Civil wars can go on for many years and be just as destructive and damaging as international wars. Civil wars tend to become complicated very quickly. A civil war might start between two sides, but groups might break up and the new, different sides could start fighting each other. Groups who were not involved at the beginning can easily be sucked in, as they fight to defend themselves against both sides. Civil wars with many different sides all fighting each other have occurred. Sometimes foreign countries help one side, or different countries help different sides. This can become a proxy war.