In Captain America #332 (1987), the US government suddenly realized the present Captain America was the same Steve Rogers who had served in World War II. This led to the Captain being summoned before the Commission on Superhuman Activities, who insisted the government owned his shield, codename and costume and if he wanted to remain using those three things, he would willingly return to the government's employ. Cap considered this overnight, then chose to surrender his costume and shield to the Commission and walked away (an outcome the Commission was in no way prepared for). To get around the government's claims to his costumed identity, Steve began calling himself "the Captain" and donned a costume with a different chest symbol and no colour blue. Still, he lacked a shield.
At the same time, Tony Stark had provided refuge for an armored super-villain named Force so that he could evade being killed by his employer Justin Hammer. As part of the deal, Force had to surrender his armor to Stark. While analyzing the armor, Tony was shocked to recognize circuitry which was supposed to be unique to his Iron Man armor. While putting his lawyer to work on the matter, Stark ran an illegal computer tap into Hammer's system and learned Hammer had only recently obtained the plans and begun selling them to criminals to improve their armors. Stark was mortified to think that criminals could be killing people with his technology as he'd deliberately given up weapons dealing on that very principle. Further, Stark's lawyer wouldn't be able to summon Hammer to court for years and all the evidence Stark had was illegal. To control the situation, Stark began hunting down the villains he'd identified in Hammer's data.
Unfortunately, Stark didn't have a complete list - he was missing one person and thought it might be the hero Stingray, who was both an Avengers ally and a U.S. Coast Guard official. When Stingray refused to relinquish his armor, Iron Man knocked him unconscious, then discovered Stingray's suit had none of his technology. Stark had only one option now: he publicly declared Iron Man had gone rogue. Thus, Iron Man would continue the Armor Wars without implicating his other identity. In fact, Stark decided to expand the scope of his mission, targeting S.H.I.E.L.D.'s Mandroid armors as he didn't think he could continue to trust S.H.I.E.L.D. with his technology (pragmatic, considering S.H.I.E.L.D. had earlier attempted a hostile takeover of his company, then tried to confiscate his armors during his alcoholism; S.H.I.E.L.D. would be revealed as almost completely corrupt shortly afterward). But Iron Man's next target was the Vault, the maximum security prison for super-criminals in the US. Policing the Vault were a small army of Guardsmen, whose armors had all been built by Stark.
Re-enter the Captain. Steve asked Tony if he could build him a new shield. Tony agreed and fashioned one from Adamantium, insisting Steve take it for free as it would be good for his company's public relations. Secretly, Tony considered this a bribe as he knew Steve wouldn't approve of his next maneuver. Sure enough, as Tony and his friend James Rhodes were en route to the Vault, they were confronted by Steve in a diner. While Tony still claimed the Armor Wars were being fought by a rogue Iron Man, Steve knew better. Tony briefly called off the assault.
Of course, he couldn't be permanently deterred; using a knock-out gas through the Vault's filters, Tony knocked out most of the guards and began deactivating the Guardsmen armors. The final Guardsman was defended by the Captain himself, who had donned a gas mask. The Guardsman began to asphyxiate within his armor but refused to surrender to Iron Man. When the Captain turned his back to help the Guardsman, Tony took the opportunity to strike the Captain down from behind. As the stunned Captain lay helpless on the floor, watching as Iron Man wrecked the last armor (while removing the Guardsman's helmet so he wouldn't suffocate), the Captain shared a last look at Iron Man:
"No words are spoken; none are needed for both men know that a bond has been borken today... a bond as old as their friendship... as deep as their innermost thoughts. A dear and precious link... that may never be whole again."
Iron Man's actions caused a breakout of super-villains from the Vault, which was a pretty bleak bit of business considering Iron Man had been motivated by a desire to stop criminals - and now had been fighting heroes while enabling criminals! After helping to catch (most) of the escapees, the Captain returned to Stark; needless to say, he returned the shield (the Black Panther provided the Captain's new Vibranium shield). Shortly afterward, the Avengers ejected Iron Man from their membership. The Armor Wars finally ended with Iron Man's seeming death, when in reality Tony had survived and soon built a new Iron Man armor. As before, Tony claimed Iron Man was his employee and bodyguard and that this Iron Man was (obviously) a different person from the (supposedly dead) rogue Iron Man. In reality, Tony had gotten away with everything: he'd defeated his enemies, waged war against S.H.I.E.L.D. and federal law enforcement, knocked the Captain out from behind and even killed one of enemies (Titanium Man) and without any consequences.
Of course, Steve knew the Iron Man who knocked him out was Tony Stark and he seriously doubted Tony had given up being Iron Man since the Armor Wars. In Iron Man #238 (1989). Steve and Tony convened a meeting, but Tony still maintained he wasn't Iron Man. Tony wondered if their disputes would endanger other people when Captain America and Iron Man had to fight side-by-side. "I'm a practical man, Tony," Steve answered. "I like to think I'm a just one as well. If it comes to that, I'll lay my life on the line for Iron Man." Not long afterward, Iron Man rejoined the Avengers, still claiming to be a different person than the previous Iron Man. Most of the Avengers doubted this and constantly wondered at the truth. By deception, Tony had regained his position within the Avengers. Soon, he would abuse it.
Tomorrow! Pulling rank.