Yes, you must improve your comprehension skills and pay close attention to the Society's reply to your letter and to my posts mon this subject.
Chronology is a complex subject and not for the faint-hearted, further, it requires the skills of an exegete as many of the relevant texts are difficult to interpret so one must consult scholarly journals and Bible commentaries.
Jer. 25:11 describes the period of Babylonian domination over Judah and the nations for seventy years concurrent with Judah being desolate for that same period of seventy years. The following verse, vs12 begins a new pericope with the judgment of Babylon the city, its King and the land which commence after the 70 years was completed which would be 537 BCE and not before such as 539 BCE.
Babylon being called to account began after the 70 years was fulfilled and not before and such accounting is descriptive of that land becoming desolate as with the other nations including Judah.
You ask 2 questions and my answers are as follows:
A.1. Babylon was a World Power for 68 years 607 BCE-539 BCE
A.2. Unknown as there is no historical information for those nations with the exception of Judah whereupon we have the 70 years of Jeremiah-servitude, exile, and desolation which ran from 607 BCE until 537 BCE and a further 10 years of vassalage to Babylon which increased the totality of servitude of Babylonian domination to 80 years to be historically accurate.