Atlantic and Pacific Canal
I'm pretty sure (1) Trade with Asia is right because the plague was carried by rats on ships coming from the East to the West.
Also, you can guess by the dates. The Black Death was in the 12th and 13th centuries, while conquest of Japan and exploration of the Western Hemisphere were in the 14th century.
The United States emerged from the war as a world military and industrial leader. Unlike the war-torn cities of Europe the homes and industries of the nation were relatively unscathed by the Great War. The late entry of the US meant that fewer men had lost their lives than in Europe
