The first map shows Shia (Shiite) Iraqis with green, Sunni Iraqis with yellow, and Iraqi Kurds (Sunni) with blue. The white areas are mostly under populated deserts controlled by the Sunnis.
The reason there is this great mix in Iraq is that it is for Iraq that the Shia-Sunni split was made. In 1500 A.D. Iranians (Persians) were Sunnis, but their leaders converted their people to Shia, in order to have a strong identity to fight the Sunni Ottomans (Turks) and take control of the fertile lands of Mesopotamia between rivers Tiger and Euphrates.
The second map shows Mesopotamia, which is also called the “cradle of civilization”.
See the following article.
“This 16th Century Battle Created the Modern Middle East”, August 2014