What was the story in Marvel's The Avengers?
The basis of the movie is to form a team of "enhanced" beings, solo heroes in their own right, but "freaks" (Hulk, Thor), misfit shadow organizational agents (Black Widow and Hawkeye), an uncontrollable eccentric weapons genius (Iron Man) and a Super Soldier from a different era (Captain America)- all of whom are assembled by Nick Fury, a seasoned and personally experienced agent with expert military background, who believes that earth and mankind is insufficiency prepared to defend the planet from threats not from this earth.
Parallel to his efforst to assemble "the world's mightiest heroes", Fury continues his work on developing weapons technology from one of the Infinity Stones taken from WW2 , in the form of the cubic Tesseraxt, whom Germany's Red Skull had already manufactured a limited supply of remarkable Infinity Stone energized weapons.
The controversial issue that was so integral to Iron Man's origin to stop "making more weapons to keep us safe" is sowed and exploited by the God of Mischief in order to pre-empt the Avengera from coalescing to stop him. The near meltdown of the team was almost successful until the death of Agent Coulsen acted as a catalyst to help the team gel and come together against Loki.