
1) Adventurous ones 2) Avant-garde 3) Boone and Bowie 4) Cather subject 5) Christian missionary society 6) Covered-wagon folk 7) Early people on the frontier 8) Explorers of the unknown 9) First settlers 10) Goes first 11) Groundbreakers 12) Innovates 13) Ones who forge new territory 14) Settlement inhabitants
Found on
https://www.crosswordclues.com/clue/pioneers

1) Breaks new ground 2) Innovates 3) Settlers 4) Trailblazers 5) Trailwindbreakers
Found on
https://www.crosswordclues.com/clue/pioneers
[missions agency] Pioneers is an international group of Christian missionaries seeking to spread Christianity to people in places where other missionaries have not gone or churches are rare. It was founded by Ted Fletcher in 1979 and has offices in Orlando, Florida, Melbourne, Australia, Accra, Ghana, Dorchester, Ontario, Auckland, New Zeal...
Found on
http://en.wikipedia.org/wiki/Pioneers_(missions_agency)

former Soviet organization for youth aged 9 to 14, closely associated with the Komsomol (q.v.) for youth aged 14 to 28.[1 related articles]
Found on
http://www.britannica.com/eb/a-z/p/70

Postcards issued before the Act of Congress in 1898. They carry instructions on the back, such as, Write the address only on this side
Found on
http://www.encyclo.co.uk/visitor-contributions.php

Soviet youth organization for kids in middle grades; members wore iconic red neck scarves.
Found on
http://www.pbs.org/pov/myperestroika/glossary/

People who traveled the Oregon Trail in the 1800s
Found on
https://sciencetrek.org/sciencetrek/topics/horses/glossary.cfm
No exact match found.