I won't be commenting Ukraine situation here (I think politics and religion are best avoided on online forums, if possible).

However, I have a feeling not everyone might know the history of US foreign policy (and resulting military actions) that well. Here are couple of documentaries that - even when not perfect - give some rather good explanation as to why US is in the position they are today:

The Fog of War - http://www.imdb.com/title/tt0317910/
Why We Fight - http://www.imdb.com/title/tt0436971/