World's largest anniversary card?

On the 150th anniversary of American Independence, the United States received a birthday card from the people of Poland. Today it's preserved in the Library of Congress. The Polish Declaration of Admiration and Friendship was more than a Hallmark moment.

                                                                                                                   Library of Congress
It was presented to President Calvin Coolidge in 1926, partly in gratitude for American aid during the Great War. It has 30,000 pages (extra postage required) which are rich in color, history, pressed flowers, drawings from famous Polish artists, and notes from military and business institutions. It was delivered in 111 volumes, and signed by (are you sitting down?) 5.5 million Polish people.