It was a different era, but not every battle was waged with fire coming down from heaven or with ten divine plagues. Sometimes the Godly had to actually go out and do it.
And those who think Jesus just sat around in the meadows petting sheep, feeding the 5000, and endlessly preaching the Beatitudes just aren't reading enough.
There was evil in the Old Testament, and there's evil today.
There will always be evil on earth, therefore, war will always be necessary.