I Swear I'm Not a Byzantophile
Formed the Byzantine Empire
To fulfill the Achievement I Swear I'm Not a Byzantophile, Greece must control all territory required to form the Byzantine Empire. It the states that must be controlled are all the Greek, Turkish, Bulgarian and Yugoslav states, Albania and the states of Southern Romania (Banat, Oltenia, Muntenia and Dobrudja).
As Greece, boost popularity of Fascism, Why you ask? It is because you can get into a faction with Italy and take Albania. As soon as Greece changes ideology, improve relations with Italy, justify and declare war against Yugoslavia. After Yugoslavia capitulates, justify against Turkey. Prepare against naval invasions because Turkey will have a slightly stronger navy than Greece. It may be easier to use the Bulgarian land to encircle the Turkish army. Once the bulk of the Turkish army is encircled and overrun, push through Anatolia and the Bosporus Strait. As well as try to join the Axis so you avoid a war
After Turkey capitulates, Italy will be annexing Albania and Bulgaria It is recommended to not join the Allies. This is in case some of the territory required falls to the Soviets. A while later, Romania will join the Axis as well. It may be beneficial if land forts are placed on the border from Albania to Romania. Wait it out until the Germans declare against the Soviets. Join the Comintern when this happens. With Soviet help, it may be easier to push against the Axis. Make the push for the required states, But you can still push with the axis
With the BFB DLC you can just go do the far left side of the tree and annex Turkey allowing for you to get the achievement without all of this.