Would it be a religious duty for all the Muslims in all countries, whether young or old, infantry or cavalry, to resort to jihad with all their properties and lives, as required by the Quranic verse of Enfiru, if the Sultan of Islam declares war and calls the entire population under arms, when there is an enemy attack against Islam and Islamic countries are extorted and pillaged and Islamic people are enslaved?
Answer: It would.
In this way, would it be a religious duty for them to declare war against Russia, Britain and France and their helpers and supporters, who are enemies of the Islamic Caliphate and trying to –may God forbid- extinguish the divine light of Islam by attacking the seat of the Caliph and the Ottoman nation with battleships and land forces?
Answer: It would.
In this way, when success depends on all Muslims to resort to jihad, would it be a sin and a major rebellion if they –may God forbid- refuse to do so and would they deserve the wrath of God and the punishment for this great sin?
Answer: They would.
In this way, would the above mentioned state, who are fighting against the state of Islam deserve to be killed and burn in infernal fire if they, deliberately or under coercion, murder Muslim people, destroy their families and fight against the soldiers of the state of Islam?
Answer: They would.
In this way, would the Muslims living under the sovereignty of Britain, France, Russia, Serbia, Montenegro and their supporters deserve sever suffering if they fight against Germany and Austria, who are helping the Ottoman government, because it would be harmful for the Caliphate of Islam?
Answer: They would.
Above is an English translation of the Fatwa issued by the Ottoman Empire after its entry into the first world war, and since I've been reading a book about the Berlin-Baghdad railway and German-Ottoman relations, I've been curious as to its potential impact. Now, IRL this call really didn't have much of an impact; most Muslims remained loyal or at least co-operative with the Entente colonial/regional governments, and would fight or work for them throughout the course of the war, fizzling out Kaiser Wilhelm's dream of a great uprising by his "friends" in the Muslim world ripping apart his rivals' Empires. For the sake of discussion, however, what if for whatever reason (A more successful campaign of Pan-Islamism by Sultan Abdul Hamid, perhaps. Maybe backed covertly in previous decades by German gold?) the Ottoman call to Jihad was more widely answered?
I'm not under any impression this would create some kind of unstoppable wave of suicidal Muslim zealots which would easily sweep over local Russian, British, and French garrisons (That would require more arms and organization then they likely have), but a combination of revolts, protests, sabotage, and mass civil disobedience in areas such as the Raj (at least in regions with a large Muslim minority), Egypt, French North Africa, and the Caucuses, as well as a strong surge of pro-CP feelings among other Muslim nations/subnations (Afghanistan, for instance) and the butterflying away of the Arab Revolt. How and to what extent would this impact the logistics and war capabilities of the Entente nations? What would their responses be, and what would the results be in other theaters as a result?