It could possible be ironic and problematic because the rest of the world was technically already "discovered", but just not by the Europeans specifically.
Nickname comes from his mentor, Andrew Jackson, who was called Old Hickory. Polk entered Congress in 1824, when Jackson won the popular, but not the electoral vote to John Quincy Adams. When Jackson won both, in 1828, Polk became his protege.
<span>B. Announcement of the Marshall Plan I think</span>