The highest choice?

So I was thinking today about nonviolence and how (or if) it could be effective against something like Hitler's regime. Although my thoughts didn't lead me to any substantial conclusion, here's what I got: In the vast majority of cases (99.9%) nonviolence is probably the highest choice. However, given this reality, this world, and the people that inhabit this world, there is a chance that a situation gets to the point that there is no nonviolent solution.

Of course, this depends on the people and events surrounding the situation but if the people aren't willing to listen and if the events have picked up a momentum of their own, then the choice seems to be either continue an ineffective nonviolent protest and watch millions more people get killed, or do what is necessary to stop the killing. I suppose you could call it 'feeling the moment'. We all set boundaries but those boundaries need to be flexible and able to change with each situation. When you set the boundary of nonviolence and commit yourself to a nonviolent lifestyle, it seems almost inconceivable that you would ever again consider violence as an acceptable solution. Maybe you can't and that's okay also.

But the question still remains - what do you do about a Hitler? I'm not a history buff but even I know that there were *many* missed opportunities to stop him and prehaps prevent WWII. However, those opportunities were missed and we found ourselves in a horrendous situation. If you are committed to nonviolence, can you change that boundary to condone violence in such an extreme situation? Does that negate all your other nonviolent efforts? When do you draw the line again? If you cross that line once, isn't the tempation always there to cross it again? Can you condone violence done for even such an extreme purpose?

Obviously. this line of thought led only to more questions. I'm sure this subject will come up during my studies and I look forward to hearing others' opinions and insights.