Grief and outrage scarred the years 1968 and 1969, when the assassinations of Dr. Martin Luther King, Jr., and Robert Kennedy cast the nation into a prolonged period of tumult and self-examination. At the same time, the extraordinary achievements of NASA's Apollo 8 mission, putting astronauts into lunar orbit, and Apollo 11's landing men on the surface of the moon inflated the nation's sense of pride.
At the Post Office Department (POD), significant changes occurred during this same time period. For instance, the POD introduced Priority Mail service as a subclass of First-Class Mail in 1968. Further, during Richard Nixon's first year in office, under the direction of Postmaster General Winton Blount, political patronage for appointments to postmaster and rural carrier positions ceased.
The stamps issued during this period commemorate the historic origins of the United States, including the Historic Flag Series and stamps honoring pioneer explorers Father Jacques Marquette, Leif Ericson, and Daniel Boone. Conservation, nature, and natural history themes had prominent representation among the period's stamp issues. The Beautification of America, Botanical Congress, and Wildlife Conservation Issues were among the stamps depicting these themes.