We are now entering the book of Ezra! In chapter 1, we find the Israelites in captivity. They are part of the Persian Empire ruled by Cyrus, and he seems to be a pretty powerful man.
Ezr 1:1 Now in the first year of Cyrus king of Persia, that the word of the LORD by the mouth of Jeremiah might be fulfilled, the LORD stirred up the spirit of Cyrus king of Persia, that he made a proclamation throughout all his kingdom, and put it also in writing, saying,
Ezr 1:2 Thus saith Cyrus king of Persia, The LORD God of heaven hath given me all the kingdoms of the earth; and he hath charged me to build him an house at Jerusalem, which is in Judah.
However, even though he was such a powerful man, God was still able to influence him by steering his spirit. I have to imagine that being the king of Persia meant that he was a pretty strong-willed individual. He must have gotten to the top by showing quite a bit of ambition and mental strength. Regardless, he was powerless to resist the call of God even though I have to imagine that he would have resisted letting part of his kingdom wander back to their homeland.
He was also powerless to resist the call of God even though it probably flew in the face of everything he believed as well. Judaism was not native to Persia, and as far as I know, Cyrus was not an active practitioner. In these verses, he obviously recognizes God, but I have to imagine that he probably had a pantheon of other deities that he believed in.
For both of these reasons, there was probably not very much incentive for him to actually encourage someone to go back to Jerusalem and build the second Temple.
He did order that though, and I think that that is an example of how powerful God is.
We generally think that we are going to do what we want to do. The human will is perceived to be a pretty powerful force. However, in reality, God is so far above all of that. He doesn’t really care about what is “expected” on earth. He does what is in His will.