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 or Communism. As soon as Greece changes ideology, justify and declare war against Bulgaria. After Bulgaria 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.
After Turkey capitulates, prepare for war against Italy and the Axis. Italy will be annexing Albania and Yugoslavia and will soon be going to war with Greece via their national focus. 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. If the Soviets take required Romanian states, give states that are not needed and ask for control for the required states. As soon as the required states are in Greek control, click the Restore Byzantium decision.