They may not have been "uniquely" expansionist, but they were easily one of the most expansionist civilizations/empires to ever exist.
I take big issue with calling them "devoted to peace". The same as I'd take issue with calling Mongols, Romans, or Alexander's Greeks/Macedonians being called "devoted to peace". They very obviously were not. For selfish reasons, they provoked a staggering level of warfare, on a totally different scale as the typical kingdoms that existed throughout the world.
I take big issue with calling them "devoted to peace". The same as I'd take issue with calling Mongols, Romans, or Alexander's Greeks/Macedonians being called "devoted to peace". They very obviously were not. For selfish reasons, they provoked a staggering level of warfare, on a totally different scale as the typical kingdoms that existed throughout the world.