to encourage the american people to support the world war i effort, government posters and advertisements…

Brief Explanations:

During World War I, the U.S. government used propaganda to rally public support. Posters and advertisements often emphasized themes of patriotism, such as duty to country, sacrifice for the nation, and the importance of contributing to the war effort. This was a common and effective strategy to boost morale and encourage enlistment, war bond purchases, and other forms of support. Pleas from soldiers were less common as a primary theme compared to overarching patriotic messages. Images of movie stars were not a typical feature of WWI - era government - sponsored war propaganda. While the president might be associated with the war effort in some contexts, the broad and unifying theme of patriotism was more central to the majority of government - produced posters and ads.

Answer:

themes of patriotism.