The pivotal argument against the concepts of “Manifest Destiny” centered around the idea of imperialism and its moral implications. Critics, including writers like Frederick Douglass and politicians, argued that it justified the expansion of U.S. territory at the expense of indigenous peoples and Mexican sovereignty. They highlighted the negative consequences of such expansion, including war, displacement, and the contradiction of American values like liberty and justice for all. These voices emphasized that relying on notions of divine right to expand was unjust and detrimental, fostering a deeper debate about national identity and morality in U.S. policy.