At what point should the US get involved in global or foreign affairs?

Full disclosure, I’m not a Libertarian, but would genuinely like to know your perspectives. The Russian invasion of Ukraine is obviously wrong, but my assumption is that most here would be opposed to intervention by the US with military action.

Is that because we aren’t directly threatened/impacted by this? Would it matter if Russia (or China, if you prefer) invaded our neighbors to the north or south?

I think war should be a last resort, but when should it be on the table (if ever) with conflicts that do not include a direct attack on US soil?