This is obviously easy to say in hindsight, but yes more could have been done. Hitler and the Nazi army slowly but surely put their plan into action, and they were appeased at every step until it was too late. Everyone wanted to avoid war, so they let Germany slowly take too much control. If countries stepped in earlier, the extreme damage could have been prevented.
It is hard to say one way or the other. I believe it would of been less tragic if a country stepped in sooner to help, but I am not sure it would of flat out been prevented. It was a difficult time with many evil people doing terrible things.