There is a duck in every game. You may not see it, but it's there.
In practice, it is a very rare occurrence: Usually players have sufficient resources at their disposal to oust the invaders swiftly. A combined attack is something else, though, but if multiple players zoom in on another like that, he probably deserved it.
Babylon had the audacity to build 3 heroes and was heading for the fourth. Thus, Carthage and Greece had to take him down and quickly. That's why he was almost wiped from the baord and had his capital in danger of being converted. Carthage chose to occupy instead as we could not fin the rule (I'm glad we played it correctly). Of course, then rome won with 4 heroes in the next two turns due to turtling with his armed forces. His First wonder was the statue of Zeus. Thus, he barricaded all his forces and waited for a distraction to cement his victory.