May I suggest learning more about the Pony Express on the National Postal Museum's website? It's one of my favorite Smithsonian Institutions! I recommend taking a look at the Systems at Work exhibition, where there is a video about how mail is shipped by the United States Postal Service. Did you know that Postal Service was established in 1775? That makes it a year older than the Declaration of Independence! It's true - and the first Postmaster General was Benjamin Franklin.
Showman and Congressional Medal of Honor recipient, Buffalo Bill Cody claimed that he was one of the original riders of the Pony Express, but without any remaining employment documents, this can't be confirmed. There is an American Experience you can watch on Buffalo Bill and his Wild West show.
The Marshall Plan is named after George C. Marshall, who was Secretary of State from 1947-1949, during the Truman administration. Before this position, Marshall was the Chief of Staff of the Army during WWII. He saw the level of destruction that years of war caused throughout Europe, and knew that it would take a lot of money to rebuild cities and countries. Fighting did not take place in the continental United States, so after the war, America was very prosperous. Marshall designed the European Recovery Plan (original title) to help our friends, allies, and former enemies, rebuild their countries and industries. The Marshall Plan changed the outlook for those European countries, but also helped America by creating good will between nations, and an opportunity for us to sell goods overseas.
$15 billion dollars in 1948 is now worth over $167 TRILLION dollars. (I love the Inflation Calculator!)