What exactly do the Avengers avenge?

Thank you all for your 173 pageviews which I always stress means ALOT to me! I just watched The Dark Knight Rises last Saturday, it was EPIC! But that movie effectively closed the superhero movie season for this year. So now I'm gonna dig back and talk about the movie that started this year's superhero season, the Avengers.(What do they avenge anyway?) Warning: This IS going to be a spoiler review,but you can't blame me for that,its July and you should have already watched this great movie. The Avengers storyline is pretty basic,with the villain, Loki,Thor's brother, coming to Earth with an army of Chitauri behind him to get the Tesseract and destroy Earth. At the end though we see he's actually taking orders from Thanos(probably villain for the next Avengers movie.I enjoyed this movie,despite some flaws, though the flaws are minimal.The roster for this movie is Captain America, Iron Man,Thor,Hulk,Hawkeye and Black Widow. The thing I like was that the characters were already established of being in a same universe, which I think is the first time in history that has ever been done. Sure it took a LONG four years, but it was worth every second. The biggest gripe I have with this movie is Hulk,or at least Bruce Banner's explanation on how he controls the Hulk. Don't get me wrong, I prefer Mark Ruffalo over Edward Norton as Bruce, but the "I'm always angry" line doesn't make sense to me. Can any of you tell me what that meant? The next gripe was the way the Chitauri were beaten. They had an epic battle, but when I saw it for the second time,it seemed like the almighty galactic army were taken down by a nuclear missile. Heck if that was true just send Iron Man to fire it and be done with it. The next gripe could be considered nit-picking but I'm still gonna list it anyway. While the Avengers were busy fighting and all, where the heck was S.H.E.I.L.D and Nick Fury? I mean I know they aren't powerful, but they could give help in numbers, for god's sake its 6 Avengers against a whole army while the most powerful secret agency on the planet doesn't do anything! But in the end, I feel the movie pro's FAR outweigh the con's, and since there are too many, I'll list out a few(though the best way to know is just go WATCH the movie): Mark Ruffalo's stellar performance(I note him because I was most worried with the constant recasting of Hulk), each of the Avengers get enough screen time(yes even with 6 bigger than life characters, they all have distinct personalities), they had a most believable threat(a whole galactic army) and its surprisingly funny(Robert Downey Jr. was expected, but the others had some memorable moments too). The biggest PRO of the movie is that it is the first of its kind and made something that will probably change every producer's mind when making a super hero movie: a shared cinematic universe. But after rambling on about superhero movies, I feel its time for me to get back to books,or in this case,comics. So watch out for my next review on a series of comics I enjoy whole-heartedly: Pokemon Adventures(yea it was a kid's show but hey I'm still not fully a teenager yet) OK guys once again thank you for your pageviews and hopefully you'll comment on where I can improve!