Zedekiah had just been made king of Judah. From both Hebrew account and the Babylonian Chronicles, Zedekiah was placed on the throne after his brother Jehoiachim was removed from king Nebuchadnezzar. (I know it's Wikipedia but link).
Surrounding kingdoms sent diplomatic envoys to Jerusalem to establish ties with the new king. What a great time to proclaim that they should all surrender and serve Babylon! Well that is exactly the message Jeremiah sent back to the visiting kingdoms. Jeremiah then gave the same message to young king Zedekiah. What a killjoy.
It isn't even surprising to learn that Zedekiah ignored this prophecy and rebelled against Babylon nine years later. Nebuchadnezzar came to Jerusalem and it fell after a 30 month siege (2 Kings 25:1-7). Jerusalem was razed. The temple gutted. The king's house and all the other great houses were also burned down. Then the walls of Jerusalem were broken (2 Kings 25:8-12). The Babylonians were very thorough. I find it interesting that Babylon was only doing what God allowed, nothing more.
Nebuchadnezzar put him on the throne! In that way, Zedekiah was playing poker with house money. Except he had been told what everyone's cards were and how to play a winning hand. He wouldn't take the whole pot but he could still win. Instead, he ignored the game plan, bet his kingdom, and Judah lost.