According to Silver Age Marvel continuity, Captain America was frozen and presumed dead at the end of World War Two only to be revived in Avengers #4 (1964). However during the 1950's, the Captain America character was briefly revived in the comics before the book's subsequent cancellation. Stan Lee chose to ignore the revival, basically sweeping it under the rug in terms of continuity. Englehart decided to explain this apparent discrepancy, revealing that a schoolteacher had rediscovered the super soldier serum during the 1950's, and transformed himself into the new Captain America and a young colleague into a new Bucky Barnes. The two worked as Captain America and Bucky briefly during the 1950's but their transformation was flawed and both men became psychotic. The government intervened and put them in suspended animation until they were released in the 1970's. The fake Captain America and Bucky battled the real Cap and his partner the Falcon with a traditional superhero battle having an underlying examination of the societal differences between the 1950's and the 1970's.
As seen by the 1950's Cap story, Englehart wasn't afraid to explore Captain America's metaphorical potential. Since the character was always portrayed as a patriot (what else would you expect from someone dressed in red, white, and blue?) as well as a man out of time, there was considerable potential for exploring social and political issues. While Cap's writers had occasionally dealt with the changing political environment of the late 1960's and 1970's, the stories tended to focus on standard superhero fare. Englehart knew how to write engaging superhero tales but his stories were more than battles between costumed heroes and villains. The Marvel Comics of the 1960's added a personal dimension to traditional superheroes and Englehart (among several others) added a dimension of exploring society through his stories.
Englehart continued exploring social and political issues in the pages of Cap. In one memorable storyline, he had a supervillain named the Viper, a former advertising executive turned criminal. The Viper would quote advertising slogans which were popular at the time during his battles with Cap, a commentary on American consumerism. Englehart addressed social and political commentary into his stories without hitting his readers over the head.
Englehart's incorporation of social and political issues culminated in the Secret Empire storyline in Captain America #169. In this issue, Englehart brought to the forefront a group called the Committee to Regain America's Principles (which makes for an interesting acronym). For several issues, the group had been running an ad campaign questioning Captain America's role in society. This subplot came to a boil in issue #169 when Cap confronted the Committee's front man Quentin Harderman about his smear campaign. When Harderman suggests that Captain America participate in a charity boxing exhibition as a good will gesture, Cap sees this as an opportunity to sweep away any doubts about his reputation. The exhibition turns out to be a setup, with Cap discovering his opponent is actually Grade Z villain the Tumbler (and let's face it, most of Cap's villains are Grade-Z). To everyone's shock, Captain America appears to kill the Tumbler during the battle.
From there things get worse for Captain America as he finds himself on the run from the law. He then battles the Committee's hero, Moonstone, and is promptly defeated and imprisoned. With the marketing savvy of Quentin Halderman behind him, Moonstone quickly becomes a popular hero while Captain America becomes public enemy number one.
After Captain America escapes from jail, Cap and the Falcon travel the country tracking down clues that lead them to a nation-wide conspiracy. They team up with Professor Xavier, Cyclops, and Marvel Girl of the X-Men, and learn that mutants are being abducted all throughout the country. They discover that an organization known as the Secret Empire is behind things. Cap and his allies infiltrate a Secret Empire base, but are discovered and marked for death. However they are rescued by S.H.I.E.L.D. agents who tell Cap of the Secret Empire's history.
Captain America races to Washington D.C. where the Secret Empire has landed a flying saucer on the White House lawn. Moonstone attacks the saucer's champion but is soon defeated on national television. Moonstone enters the saucer where it is revealed that he is in cahoots with the man who has just defeated him. Moonstone then leaves the saucer and tells his audience that he has seen the enemy and that they are unstoppable. With America's greatest hero seemingly defeated, the nation wonders who can save them. When the Secret Empire threatens to detonate nuclear weapons that they have planted in cities throughout the United States, all seems lost.
Captain America arrives on the scene and confronts Moonstone. Moonstone accuses him of conspiring with the Secret Empire but Captain America is not there to talk. After a pitched battle (including a nice double page spread by Sal Buscema), Cap defeats him. Moonstone and Harderman turn on each other, revealing the conspiracy. Cap chases the masked leader of the Secret Empire into the White House. After a brief battle, the leader of the Secret Empire reveals his identity, telling Cap that political power wasn't enough. He shoots himself, leaving Cap stunned.