The American Football league and National Football League merged into the modern NFL in 1970.
Since the date they entered the NFL the Broncos rank as the only team in history to have never had a non-sellout at home (the Houston Texans are in this class too, but they are an expansion team with just a decade of play under their belts).
In that time the Broncos have been to the Super Bowl six times (only three teams have been to more), are tied for sixth in winning seasons with 24, fifth in overall wins (385), second only to the Steelers in home wins (221) and are sixth in advancing to the conference championship game eight times.
Quite a record.
And it has not been done just on offense.