First International Postal Conference
On May 11, 1863, representatives from 15 nations met in Paris to discuss postal issues. That first International Postal Conference would eventually lead to the creation of the Universal Postal Union.
Up until this time, mail between nations had been regulated by a number of different agreements that were binding only to signing members. At one point, Germany had 17 postal agreements, France had 16, Belgium had 15, and the United Kingdom had 12. Plus, some nations used different weight measurements – the US and UK used ounces while France used grams. This made it especially difficult to calculate the postage rates as a letter traveled through different countries.