Soft Power, by Joseph S. Nye, Jr. is a good book on the necessity for a government to use both hard (military or police) and soft (diplomacy, working together, etc.) power. His main goal is to show how important soft power is in intergovernmental affairs. It's a good book. Here's an interesting comparison on how different countries apportion hard and soft power in 2001-2;
Country Public Diplomacy Defense
U.S. $1.12 billion $347.9 billion
France $1.05 billion $33.6 billion
Great Britain $1.00 billion $38.4 billion
Germany $218 million $27.5 billion
Japan $210 million $40.3 billion
As can be seen, every country attempts to use both. Some rely more heavily on hard power than others. It's an important thing to keep in mind when considering political moves.