From The Grey House:
Mierka and Joseph finished barricading the windows, saying little. The two met during the French Revolution. She had been an exceptional spy for the Revolutionaries. Vincent and Joseph allied themselves with the nobles; the vampires enjoyed fueling the ignorance of the wealthy and deepening the Revolution. The two friends never encouraged wars between humans and HellSpawn but took great pleasure in stoking the fires of human wars. It was easier to hide bodies during wars.