Washington, D.C.
Washington, D.C. is the capital city of the United States of America, one of the most powerful nations on Earth, and the nation where the Ark lay in most Generation 1 continuities.
As a center of political power, it featured in many Transformers stories. The Dinobots once defended it from the Decepticons and the Sub-Atlanticans, without destroying too much of the city in the process. Atlantis, Arise!
On another occasion, Optimus Prime met with the President there, but Soundwave "overheard" the planning. Megatron then used the Insecticons to attack the city, framing the Autobots as the ones behind the attack. The Decepticons are defeated largely through their own ineptness, and the President saw through their ruse, anyway. Plague of the Insecticons!
