Final answer:
The strongest influence on Washington Irving's writing was European Romanticism.
Step-by-step explanation:
The strongest influence on Washington Irving's writing was European Romanticism. Irving was heavily influenced by the literary and artistic movement that celebrated imagination, nature, and the supernatural. His works, such as "Rip Van Winkle" and "The Legend of Sleepy Hollow," often featured elements of folklore, myth, and the natural landscape, which are key characteristics of European Romanticism.
Learn more about Influence on Washington Irving's writing