The document discusses several US presidential doctrines throughout history: - The Monroe Doctrine (1823) stated the US would not involve itself in European affairs and viewed further European colonization in the Americas as hostile. - The Truman Doctrine (1947) aimed to contain communism by providing political, economic, and military aid to democratic countries facing external communist pressure. - The Nixon Doctrine (1969) expected US allies to take responsibility for their own defense, with the US and UN providing support as requested. - The Bush Doctrine (post-2001) declared the US would make no distinction between terrorists and countries that harbor them, allowing preemptive self-defense actions against terrorist threats.