system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] What level does a threat have to be before the Avengers step in?

I guess this is specifically pre-Civil War, but presumably Iron Man and War Machine were still somewhat active under the Avengers title since Tony was planning on inducting Spider-Man.

In all, we see the collective Avengers in 4 battles as a team before splitting up:  the Chitauri Invasion, the battle at Strucker's Castle, the Ultron fights, and the fight with Crossbones' terrorist group.  Out of those, only the Chitauri Invasion and the Ultron fights were potentially world-ending.  The battle at Strucker's Castle seemed to be more about cleaning up Shield's loose ends, but the fight against Crossbones could be considered either that or a general battle against terrorists.

What qualifies a threat as being Avengers-worthy?  Would Cap have slipped into a telephone booth to suit up if he saw a bank getting robbed on his day off?  Did they typically only deal with groups like Hydra?  How common would a fight against something like Abomination or the Maximoff twins be?
gpt
It seems that they're a bit of a skunkworks situation. They come together when the situation warrants it and then go their separate ways. The banner always exists, but it's objectives, members and MO depend on the threat.

Fury assembled them to stop Loki, then they went back to whatever once that was over. Steve got them back together to hunt down the hydra remnants, which led directly to Ultron (Tony spends a good deal of AoU talking about making the team obsolete), but once that was handled, they stripped it down again and went back to hunting hydra (which is what they're doing at the beginning of CA:CW).

Tony says it best in IW: after civil war, they're essentially broken up. Rhodes and vision are the only real members still left and they're under the jurisdiction of the sokovia accords. The "real" team is the ones in hiding led by cap and they're likely moving around, staying off radar and helping where they can.