Complex sentence: A month later they were voted into the Big Sky Conference, effective the following July, and the Broncos began NCAA competition in 1970 in Division II ("College Division" prior to 1973) in a brand new venue.
Split into simpler sentences: A month later they were voted into the Big Sky Conference, effective July 1970. Boise State began NCAA competition in 1970 in Division II ("College Division" prior to 1973) in a brand new venue.