When, if ever, should states interfere in each other's internal affairs?

The first 200 words of this essay...

When, if ever, should states interfere in each other's internal affairs?

The issue of state interference is a hugely contentious one in International Relations. Interference occurs on a daily basis; economic decisions by one state have impacts on others, is this interference? A decision not to honour an agreement to play cricket matches in a particular state has implications, but is this interference? This essay shall limit its discussion to cases of interference, particularly of a military nature, that are purposely pursued by states to modify the internal structure or policy of another state. It is the premise of this essay that there are two clear situations in which the interference by one or more states into the internal affairs of another is justified; self defence, and the protection of human rights.

This essay shall begin with some necessary definition; of intervention, sovereignty, and human rights. These definitions are by no means accepted by all, but a general conception of such ideas, acceptable (if too brief) for most, shall be reached. It shall be seen that sovereignty in particular can be interpreted in different ways, which has an enormous impact on the contention of this essay.