Think about sending a letter to a friend in another country. You write the letter, put a stamp on it, and drop it in a mailbox. Within days, it arrives thousands of miles away. This seems simple, but making it work required one of the greatest logistics systems ever built. On October 9, 1874, twenty-two countries formed the Universal Postal Union. Before the UPU, sending mail across borders was complicated. Each country had its own rates and rules. A letter crossing three countries might need three different stamps and three different payments. The UPU created a single system. Any member country would deliver mail from any other member country for a standard price. Today, the UPU has 192 member countries. A letter goes through several steps. First, it is collected from mailboxes and sorted by destination. Machines can read addresses and sort thousands of letters per hour. Letters traveling far go by plane. Local letters travel by truck. At the destination, carriers deliver them to the correct address. The entire process, from your mailbox to someone's doorstep across the world, usually takes less than a week.