Thanksgiving is a national holiday celebrated on various dates in the United States, Canada, Grenada, Saint Lucia, and Liberia. It began as a day of giving thanks for the blessing of the harvest and of the preceding year. Similarly named festival holidays occur in Germany and Japan. Thanksgiving is a national holiday celebrated on various dates in the United States, Canada, Grenada, Saint Lucia, and Liberia. It began as a day of giving thanks for the blessing of the harvest and of the preceding year. Similarly named festival holidays occur in Germany and Japan.