Here's why there's no clear answer:
* Different Areas of Influence: Literature influences various aspects of Western culture: philosophy, art, music, politics, social thought, etc. What's influential in one area might not be in another.
* Time Periods: Influence changes over time. A literature that was extremely influential in the 19th century might have less impact today.
* Individual Preferences: People have different tastes and find different literatures more meaningful.
However, some national literatures are often considered highly influential:
* Ancient Greek literature: Foundation of Western philosophy, drama, and literary forms.
* Roman literature: Influenced Latin language and culture, legal systems, and narrative styles.
* French literature: Impact on literary movements like Romanticism and Symbolism, and on fashion and thought.
* English literature: Hugely influential in language, philosophy, and the development of the novel.
* American literature: Significant contributions to modernism, experimental writing, and social commentary.
It's important to consider that national literatures are constantly interacting and influencing each other. It's not just about individual countries, but the overall flow of ideas and artistic developments across the Western world.
Instead of trying to find a "most influential," it's more productive to explore and appreciate the unique contributions of different national literatures and how they have shaped Western culture.