The titular team undoubtedly had what Tony Stark described as "traction" issues in the first Avengers movie. There was a three-way fight between Thor, Iron Man and Captain America, Tony Stark and Steve Rogers had words with each other that nearly resulted in more brawling, and Hulk and Thor's battle nearly took down the S.H.I.E.L.D. Helicarrier. However, the "death" of Phil Coulson served as a means of bringing them together, giving them the incentive to defeat Loki and his Chitauri army. But it was all a lie. Nick Fury had secretly had Coulson's body whisked off to an operating table where Kree DNA was used to bring him back to life, while the Avengers were left to mourn his death. As far as audiences are aware, the heroes still think he is dead - and that's really not fair on them. He was their friend and, although it might make their heroics against Loki and the Chitauri seem less meaningful, they need to know he is alive. Age Of Ultron should be where it's made clear that they do.
