The player's country:
- is in the Muslim religious group.
The player's country:
You'll want both Castile and Aragon to rival each other. This way when they end up fighting each other you can swoop up and grab the European provinces. From there, it's the usual Ottoman start. Annex Byzantium, Athens, and the Anatolian Beyliks. Set your national focus to admin as you will need it. Reclaim any cores that you have except for your core in Qara Qoyunlu because you need to save your manpower. Genoa is almost always willing to give up their islands if you threaten them with war and Venice will often give up their islands to a threat of war if they are embroiled in a war themselves. Build up your armies and navy to be ready for the first war with the Mamluks around 1460.
After expanding eastwards through Anatolia, it is recommended to build a fleet of galleys and carrier ships and conquer the provinces required from Naples and Aragon, as if the player leaves it for late game it will be harder to achieve as they will be under the control of Spain through the Iberian wedding event.
Take the mission to conquer the Levant which will give you claims on all Mamluk land through to Egypt. Declare your first war and take as much land as possible. It is not possible to take all the land in one war but that is no matter. After coring the recently conquered lands, declare war on Cyprus. The Mamluks start with a guarantee of Cyprus so should come to their aid. Finish taking the rest of the Levant from the Mamluks and annex Cyprus.
After conquering the Levant and the northern Hejaz provinces look in the Arabian peninsula for a country which is now small but has lots of cores to vassalise, i.e. an empire that rose and fell. Spend the time that you have a truce with the Mamluks feeding land to your Arabian vassal.
If you have spare time during your truce you can clean up Trebizond, Aq Qoyunlu or maybe some of the Balkan nations. However, do note that this achievement still requires you to have all owned provinces in the Muslim group so you'll have to convert them later. You should also have reclaimed most of the Italian provinces around the Black Sea, Anatolia and Greece.
Land of the Pharaohs
Take the mission to conquer Egypt which will give claims on all of Egypt. Declare war on Mamluks and take their CoT's and Cairo to further inhibit their ability to defend their meager empire. After the first war, continue expanding your Arabian Vassal and begin their annexation. This is a good point at which you should have the manpower to expand into QQ. Take your core and all the northern provinces you can, avoid taking Iraqi provinces as you will get a claim on these later from the Conquer Mesopotamia mission. Declare a second war on the Mamluks and bring Egypt into your control.
At this point you should be in control of Greece, Anatolia, the Levant, Egypt, all Eastern Mediterranean Islands and most of Arabia. If you also control parts or all of the Balkans it is an added bonus. You should now start the push towards Southern Spain. In order to unify Islam you must conquer Southern Spain, Sicily and all of North Africa. You can either threaten or actually declare war on Naples and Aragon for Southern Italy and Sicily. Use your missions that give you claims on Tunisia and Tripolitania to conquer those regions, and then conquer the rest, or vassalize a Berber nation such as Algiers, which you get a mission to subjugate, and feed your vassal the rest of North Africa and then start integrating them. (Increased coring cost in North Africa affects vassal integration cost so vassal feeding does not save monarch points.)
Morocco deserves a special mention as an alternative starting nation. It has the unique ability to take on Spain early in the game, taking advantage of one of their inevitable conflicts in Europe to claim the province. Morocco also has the ability to cut through technologically inferior West African and Ethiopian tribes to Aden, leaving conquest of the Ottomans until the end. Egypt is not required for the achievement, making expansion through West Africa a cheaper option with provinces whose trade can be pulled to the player's home node.