The so-called Islamic State in Iraq and Syria (ISIS) is in fact not a State, it is intended to be an Empire, the Caliphate of Arab Islam, extending not only throughout the Middle East, but the whole world. Those who have studied history know that Empires do not last, they are too big, unwieldy and ungovernable and they break up in time into smaller units that eventually become coherent States. For example, the Roman Empire, the Arab Empire, the Turkish Empire, the British Empire, and so on.
Although the rationale for the current IS is ostensibly religion, the drive to re-establish the Arab Muslim Empire is its founding principle or ideology.. Other ideologies have had similar pretensions to be Empires, the German Nazi ideology that sought to subjugate the entire world, the Soviet Russian Communist ideology, that pretended to want to help the workers but really wanted to take over the whole world, and so on. Iran, which is the center for Shia Islam, also has the memory of the great Persian Empire as its motivation.
The modern secular nation State is the antithesis of all Empires. The USA never accepted imperialism, the control of one country over other peoples, and even during WWI there was friction between the Allies, the USA on one side and France and Britain on the other. The idea of a Mandate after WWI was invented to satisfy Pres. Wilson, that the mandatory power (Britain and France) were there as conquerors only for a limited time, during which they would work towards the self-determination of the native peoples. In the French Mandate of Syria and the British Mandate of Mesopotamia (Iraq) that was the local Arab peoples and in Palestine that was the Jews.
Note that the US never accepted any Mandate, even though they were offered in Turkey and Armenia, because Wilson did not want the US to become embroiled as an imperial power, although they did play this role in the former Spanish colonies of Philippines and Cuba. This friction between the US and Britain and France continued during WWII and the US under Roosevelt and Truman was intent on ensuring that the defeat of the German and Japanese Empires would not lead to a replacement by the British and French of an expansion of their Empires.
Logic tell us that an Arab Muslim Empire starting out in Iraq and Syria could not last. In fact the original Arab Empire lasted as a unit for barely 100 years before it broke up. However, to try to reestablish this Empire would cause so much killing, destruction and suffering, that it is absolutely necessary that all the civilized nation states of the world band together to defeat it. That means NATO and the Russians and many others need to pool their resources and coordinate their military attacks. You have only to look at the utter destruction in Syria and also what is coming in Mosul in Iraq to know that this evil movement must be stopped.