Germany and France had 3 major wars over a period of 70 years (Franco-Prussian 1870, WWI 1914, WWII 1940) over disputed territories of Alsace-Lorraine/Elsass-Lothringen. Finally, one side of defeated, settled borders were created and France/Germany have been partners now for decades (under American protectorate).
The ethic mixing is a huge part of the problem in the war torn parts of the world, the Middle East, Africa, Pakistan/India/Afghanistan.
The West took centuries to sort this out. Central Europe took WWII to sort it our. The Balkans, Eastern Europe, Central Asia, the Middle East and South Asian are still sorting this out. It ain't pretty and it ain't gonna get any prettier.
Segregate, build fences -- sadly, that seems to be the only solution. The problem is -- which land belongs to whom. in most places "everyone" has lived or continues to live there in a mixed fashion.
but good sum-up, thank you