On December 24th 1814 the Treaty of Ghent was signed in the Flemish city of Ghent.
This was a peace treaty between the United States of America and the United Kingdom of Great Britain and Ireland which officially ended the War of 1812. The was is considered to be part of the Napoleonic Wars in Europe, but as in a war in its own right in the US and Canada.
The treaty restored the boundaries to their pre-war lines, which resulted in around 40,000 square km of the US being returned to it and the US-seized areas in Canada were also returned.
Image: By Amédée Forestier (Smithsonian American Art Museum, Washington D.C.) [Public domain], via Wikimedia Commons