We’ve all heard of the Monroe Doctrine: in his December 1823 Annual Message to Congress, President Monroe announced that “the American continents, by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European powers. . . . [W]e could not view any interposition for the purpose of oppressing them, or controlling in any other manner their destiny, by any European power in any other light than as the manifestation of an unfriendly disposition toward the United States.”
Early in Theodore Roosevelt’s presidency, Britain, Italy, and Germany jointly blockaded Venezuela’s ports to demand the payment of foreign debts and private damages owed to their citizens. An international arbitral tribunal gave preferential treatment to the blockaders over creditor nations that hadn’t displayed such militancy. Roosevelt feared this ruling would encourage Europe’s great powers to seek redress from delinquent Latin American nations through direct intervention. Recalling that Monroe had once inveighed against European intercession in the Western Hemisphere, Roosevelt deduced a corollary from this celestial principle and articulated it in his December 1904 message to Congress:
Chronic wrongdoing, or an impotence which results in a general loosening of the ties of civilized society, may in America, as elsewhere, ultimately require intervention by some civilized nation, and in the Western Hemisphere the adherence of the United States to the Monroe Doctrine may force the United States, however reluctantly, in flagrant cases of such wrongdoing or impotence, to the exercise of an international police power.
Before my internship, I had no idea what these annual messages (what we now call State of the Union messages) looked like. My sample size is tiny, but most of the ones I saw (almost all before 1900) were either incorporated in larger bound volumes or stored alone as billowy bundles of paper. Roosevelt’s 1904 Message was printed as a compact booklet with a black leather cover:
Edit: You can see the Corollary passage here.