Turkey population was just 17 million in 1939 ??? That is shocking. It is also surprising to see Germany and Russia's population is lower today than 1939!
Yupp.
Turkey did suffer from WWI heavy losses. The number you see includes millions of European Muslim refugees (Albanians, Bosnians, Pomaks, Torbesh, Gorani, Muslim Greeks...) and Muslims from territories under Russian occupation like Chechens, Ingush, Avars, Dargins, Lezgins, Tsakhurs, Circassians, Abasins, Azerbaijanis, Kumyks, Karachays, Balkars, Nogais, Muslim Tats, Digor Ossetians and so on.
Everyone has blended into Turkish society and is woven into our strong national identity. This is why many Westerners observing the PKK and Turkish state conflict often miss the point that the nation-building efforts in Turkey have been largely veru successful, even with the PKK's terrorism.
The population surged mainly due to:
1. our non-involvement in WWII
2. the immense agricultural potential of Anatolia that was previously untapped
3. government initiatives aimed at repopulating Anatolia.
We simply had time, food and space to repopulate in an era where there was no internet or social media.