Therefore — This agrees with the history. Babylon being surprized by Cyrus, when they were in deep security.
Related Commentaries of Isaiah 47:11
Isaiah 47:11
11 Therefore shall evil come upon thee; thou shalt not know from whence it riseth: and mischief shall fall upon thee; thou shalt not be able to put it off: and desolation shall come upon thee suddenly, which thou shalt not know.