Questions & Answers about Bu bölgenin modern olduğunu düşünüyoruz.
Why do we need the word olduğunu here? Can't we just attach a suffix directly to modern?
Why is the subject of the clause bölgenin in the genitive case instead of just bölge?
In Turkish factive clauses made with -dık, the clause acts structurally like a noun phrase. The subject of that clause (the region) becomes the 'owner' and takes the genitive case suffix -nin, while the verb takes the possessive suffix -u. It functions literally as 'this region's being'.
What exactly are the suffixes at the end of olduğunu?
It breaks down into olduk (the factive participle) plus -u (3rd person singular possessive, matching the region) plus -n- (a buffer letter used after 3rd person possessive suffixes) plus -u (the accusative case marker). Notice that the k in olduk softens to ğ because it is followed by a vowel suffix.
Why does the clause need that final accusative case marker?
The entire clause Bu bölgenin modern olduğunu functions as the direct, specific object of the main verb düşünüyoruz (we think). Because you are thinking a specific defined thought, the entire clause requires the accusative case.