Why is there no Czechoslovakia any more. The Czech and Slovak nationalities (tribes) wanted to be independent states.
The Middle East is much the same; their international boundaries are artificially made by Westerner outsiders as well as indigenous dictators and strongmen. Iraq is not a country with a border defined by a united people.
The Czechoslovakia example was by peaceful agreement. The Iraqis have been embroiled in a civil war for years -- a violent example of asynchronous warfare.
There needs to be a Sunni, Shia, Kurdish homeland with respect for the minorities in the region. But those groups have to agree to a peaceful settlement for this to ever happen. The Middle East has been fighting for thousands of years so I doubt we will ever see this in our lifetimes. Under the Ottoman Empire regional borders were better respected and there was relative peace for many years. But this was decreed by the Sultan -- the all powerful "king" of the Ottomans.
The Treaty of
Sèvres after WWI created the current mess ...
The Allied powers of WWI actions led to the rise of Hitler, Mussolini -- the second World War and the war of 911 and ISIS. WWI was a very costly war and the victors were very vindictive in the terms of surrender and settlement of borders and debts.