Answer: Depending on the time period the question references, Carthage may be a good answer.
Step-by-step explanation:
The Carthaginian Empire was ultimately destroyed by the Punic Wars, which marked the end of the greatest threat to Roman power over the Mediterranean at that time. It's possible that without this destruction, Rome may not have been able to grow into the great power it eventually became. Losing these wars would likely have spelled the end of the Roman Empire before it even had the chance to begin.