Are you sure Mike? Apparently your illustrious government department "Library of Congress" suggests otherwise.
"Spaniards celebrated Thanksgiving in Texas in 1541 "The Thanksgiving Timeline compiled by the Library of Congress says the first Thanksgiving in what now is the U.S. took place in May of 1541 at Palo Duro Canyon in the Texas panhandle. Some 1,500 men led by Spanish explorer Francisco Vasquez de Coronado participated in a Thanksgiving celebration after marching north from Mexico City in search of gold.
Following the timeline, we find that the Thanksgiving celebrated by the Pilgrims actually was No. 5 on the list of early Thanksgivings. After Texas, Thanksgiving celebrations or services were held in what now is Florida in 1564, in Maine in 1607 and in Virginia in 1610. The Pilgrim celebration came in 1621."
1517 wrote: But Thanksgiving isn't a National command, as if the State is giving a divine decree
"The traditional representation of where the first Thanksgiving was held in the United States has often been a subject of boosterism and debate, though the debate is often confused by mixing up the ideas of a Thanksgiving holiday celebration and a Thanksgiving religious service. According to author James Baker, this debate is a "tempest in a beanpot". Local boosters in Virginia, Florida, and Texas promote their own colonists, who (like many people getting off a boat) gave thanks for setting foot again on dry land. —Jeremy Bangs
The first documented thanksgiving services in territory currently belonging to the United States were conducted by Spaniards in the 16th century. Thanksgiving services were routine in what was to become the Commonwealth of Virginia as early as 1607,[11] with the first permanent settlement of Jamestown, Virginia holding a thanksgiving in 1610." (Wiki)
The "Thanksgiving Day" celebration is obviously an American tradition.
Note. If the "Spaniards" started the whole thing off - Wouldn't that make it a Roman Catholic celebration/tradition?