The mainstream Christian theology is that Jesus will return in order to wage war on non-believers and secure earth as the heavenly dominion of the believers (https://www.bibleref.com/Revelation/19/Revelation-19-11.html)
This grand battle and ultimate plundering of the spoils takes place in/near Jerusalem (https://www.bibleref.com/Zechariah/14/Zechariah-14-1.html)
One apparent prerequisite to this battle happening is the construction of The Third Temple which would, of course, require control over the region in which The Third Temple must be rebuilt -- Jerusalem. (https://en.wikipedia.org/wiki/Temple_in_Jerusalem)
Also they need to find a red cow. Then Jesus can come with his flaming sword and slaughter ~billions of people.