What were some changes in American foreign policy from 1898 to 1953?

1898 marked a significant change in the foreign policy of the United States. It was in that year that the country began growing its overseas holdings and projecting its power around the world. Much of this was the result of the modernization of the US Navy. Adopting the principles laid out by Captain Alfred Thayer Mahan that a strong navy ensured a strong nation, the United States began building more modern warships. To support a steamship navy, the country needed coaling stations strategically placed around the globe. As such, the US gained control of ports in Puerto Rico, Guam. Hawaii, and the Philippians for this purpose.
Also, at the end of the nineteenth century, the United States had very little experience in diplomatic foreign policy. There were very few professional diplomats in the State Department. President Theodore Roosevelt sought to change this. He recruited a number of statesmen to add to the diplomatic core and actively sought out new talent.
Another major change in foreign policy occurred in 1904 when President Roosevelt issued the Roosevelt Corollary to the Monroe Doctrine. This states that the United States was retaining the right to get involved in the affairs of unstable nations in the Western Hemisphere in order to keep European nations uninvolved.
Roosevelt also supported what he called "Big Stick Diplomacy." Essentially the United States would act as an international police force to put an end to unrest in the hemisphere. In practice, this heavy-handed foreign policy also served the needs of the United States, such as in issues of the canals in Panama and Nicaragua, the blockade of Venezuela, and the Spanish-American War in Cuba.
In the second decade of the twentieth century, American foreign policy took a shift towards neutrality and non-interference. President Woodrow Wilson set this isolationist agenda in an attempt to keep the country out of the conflicts that were consuming the great powers of Europe. Circumstances, particularly the repeated destruction of American ships by German U-boats, prevented the country from staying neutral and the United States did take up arms in WWI in 1917. This ended nearly a decade of non-martial foreign policy. However, the United States did not formally take up alliances with Great Britain and France.
The 1920s saw a more subtle approach to foreign policy. The United States did not enter into any formal political alliances with other countries and had little contact with the League of Nations. However, the country did use its financial influence to set a number of international agendas. The United States was particularly concerned with changing some of the practices resulting from the Treaty of Versailles and used its importance as a trade partner to achieve these ends.
Franklin Roosevelt's early presidency was characterized by the "Good Neighbor Policy." In a radical shift from the more heavy-handed policies of the past, Roosevelt pledged not to interfere militarily in the affairs of Latin American nations. This did a lot to repair the strained relations between the United States and many other countries in the hemisphere.
Roosevelt also tried to keep the country out of the Second World War while supporting Great Britain through the lend-lease program. The attack on Pearl Harbor and the declaration of war by the Axis Powers brought the country reluctantly into the conflict. The country threw itself wholesale into defeating the Axis. Unlike WWI, the United States became a fully fledged member of the Allied forces and worked closely with Great Britain and the Soviet Union to defeat their common enemies.
The post-war period was mostly concerned with issues relating to the Cold War. The United States was mostly concerned with containing the influence of the Soviet Union and preventing the spread of communism. This included programs such as the Marshall Plan which provided economic aid to rebuild Western Europe. The thinking was that economically robust nations would better be able to withstand the influence of the USSR.
In 1950, the United States and its NATO allies attempted to stop the spread of communism on the Korean Peninsula in the three-year-long Korean War. This was just the first of a series of proxy wars between the two world powers for global influence.
In short, foreign policy from the end of the nineteenth century to the mid-twentieth century went through periods of isolationism and periods broader global outlook. The United States started the period as an emerging global player just learning to flex its muscles. Fifty years later, the US was one of the most influential countries in the world with a well-defined foreign policy.
https://history.state.gov/departmenthistory/short-history/development

https://www.foreignaffairs.com/history-foreign-affairs