Economic self-interest may deter.

Throughout history the primary form of deterrence has been defences.

Effectively, this involves military defence forces.

Passive defences include fortifications, moats and natural features such as rivers, oceans and high ground, and serve to deter by making attacks more difficult and costly.

Building economic interdependency can therefore be considered as a form of deterrence.

These have been both passive and active.

Just as an employee is restrained from insulting his employer or a businessman from annoying his customer, nations may be restrained from some adventures either by the direct cost or by the harm to future trade and other economic activity that may result.

Active defences and their ability to deter can best be summed up by the quotation frequently attributed to President Theodore Roosevelt: "Speak softly and carry a big stick."

However, military capability and fortifications are not the only way, nor arguably the best way, to deter.