Steve and Tony had a political disagreement. The UN wanted to make the Avengers accountable to government oversight and control, an idea which Tony supported, Steve didn't. The Avengers split on the issue and we fought each other, and several of us who were with Steve wound up in a high security prison in the middle of the ocean. Which is how I got the mark on my neck, from a collar I got put on me there. The Avengers who were with Tony went back to the Avengers facility and tried to recover from their own literal and metaphorical bruises from the conflict. [Because it wasn't just Steve's side that had trauma loaded on them, to be fair.]