Military force has, throughout history always been a vital component that States have used as an instrument to help shape policy. It was genuinely accepted that a country's size, power and influence within the realm of international politics was largely dependant upon the military force with which a country could muster.
There are two schools of thought on the use of force; the Complex Interdependence theory, which argues that military force is becoming an obsolete means of shaping policy and the Realists who believe that military force is still an important instrument of state policy. The complex interdependent theory focuses on the belief that states are highly dependant upon each other, there are often many trade agreements between states, which need to be thought about before military force is taken, it is far easier to use diplomatic means, such as meetings and state visits to discuss policies that need resolving between two nations.
They also argue that trade and economic embargos can be placed upon certain countries; this is far easier than financing a military attack upon another state. Complex interdependence's also argue that the costs of military force both, morally, environmentally and economically are too expensive for it to be considered an effective instrument of policy.
Realists however argue that international politics is anarchic. States main aims are too look after their best interests. As most states have different ideologies on how best to run a country, war/violence between states is inevitable. Realists also argue that physical security is important to states. This means that in order for a state to feel secure, it needs to have a military presence of one sort or another to act as a deterrent or to give it some leverage; India's pursuit of a nuclear policy can be seen as a perfect example...