Nato wants to integrate all the countries around russia (but not russia), for no particular reason (not against russia, they are just collectors), russia doesn’t like this, so annexed piece of ukraine and sends weapons/troops to russia-inclined part of ukraine. They (russia, ukraine) agreed to freeze the conflict in 2015 by giving more autonomy to those parts, but then ignored it (it’s minsk agreements).

Usa sells weapons, and trains Ukrainian troops, which, due to ukraine history, partially embraced nationalism aligned with nazi-collaborators.

Russia wants written guarantees that ukraine won’t join nato, cause words to gorbachev that nato won’t expand in the east obviously didn’t work. Nato (usa) says they cannot guarantee that. So russia continues slow conflict in the east, which by the nature of usa supplied weapons/implied support flares up periodically