LONDON — In 1970, the Native American leader Wamsutta Frank B. James was asked to give a speech at a state dinner in Plymouth, Mass. It was 350 years since the arrival of the Mayflower, and Mr. James, a member of the Wampanoag tribe that has inhabited what is now Massachusetts for 12,000 years, was invited to participate in the commemorations.

“This is a time of celebration for you — celebrating an anniversary of a beginning for the white man in America,” his speech began. “We, the Wampanoag, welcomed you, the white man, with open arms, little knowing that it was the beginning of the end; that before 50 years were to pass, the Wampanoag would no longer be a free people.”

But that speech was never delivered. The event’s organizers had asked to see an advance copy, and proposed an alternative text. Mr. James chose not to participate. He led a protest near Plymouth Rock instead.

Fifty years have passed, and commemorations for the 400th anniversary of the Mayflower crossing are now approaching. This time, Native Americans — particularly the Wampanoag Nation — are actively shaping the programming of events in the United States and Britain.