Pereira, Diego. “A ‘Dark Root’ of Global History: Contributions Made by Oswald Spengler and Arnold Toynbee”. Brazilian Journal of International Relations 10, no. 3 (dezembro 30, 2021): 677–698. Acessado outubro 4, 2023. https://revistas.marilia.unesp.br/index.php/bjir/article/view/11073.