Why Did the U.S. Senate Have a Major Foreign Policy Role Before Senators Were Directly Elected?

Before the Seventeenth Amendment, state legislatures chose U.S. senators. Yet the Senate had a substantial role in foreign affairs, including treaty approval. How did that arrangement work in practice when senators were not chosen by a direct popular vote?

I’m curious how Senate treaty ratification fit alongside the president’s role in diplomacy, and whether indirect selection changed the way senators handled foreign policy. Was this an intentional balance between the states and the executive, or did the Senate’s influence grow through political practice?