The US Constitution limits the power of the president as comander in chief by giving Congress the ability to declare war.
The President of the United States cannot declare war without Congressional approval. The President does have the ability to put troops in another country for 60 days. However, if he/she does not get approval for those troops to be there, they must be removed within 30 days. This ability to check the power of the president is part of the checks and balance system established in our constitution.