Final answer:
Antonín Dvořák's strong sense of nationalism influenced Aaron Copland's use of American motifs and folk songs in his compositions.
Step-by-step explanation:
The strong sense of nationalism that influenced Aaron Copland's use of American motifs and folk songs can be attributed to Antonín Dvořák. In the late 19th century, Dvořák, a Czech composer, emphasized the importance of incorporating elements of one's national culture into music. His ideas greatly influenced Copland, who sought to create a distinctively American sound by incorporating American folk songs and motifs in his compositions.