WAR ALWAYS HAS A purpose. It is an organised group activity undertaken for policy ends, a conscious and rational attempt to use military force to secure a desired end-state that extends beyond victory on the battlefield. The intent may be to repel an aggressor, seize territory or overthrow a regime, weaken the position of a rival power, or compel an adversary to modify their behaviour. Broader objectives may be to achieve greater security, increase stability, or enhance influence and power. In most circumstances governments view the employment of military force against other states as an option of last resort. War is a violent activity that causes death, damage and displacement, and requires a high level of political and economic commitment. The costs of defeat are high, with a whole range of negative outcomes possible: occupation, regime change, territorial dismemberment, dismantling of military capabilities, economic sanctions, and criminal prosecution of national leaders. While major powers defeated in wars against weaker opponents may be spared some of the worst of these consequences, even they are not immune from short- and long-term damage. Their publics may undergo a crisis of confidence, incumbent governments can be vulnerable, and the armed forces may suffer a loss of credibility.

The broader effects of war are unpredictable and by no means guaranteed to be advantageous, even for those who achieve their immediate objectives. Wars can alter the balance of power and rearrange the political landscape, both in the regions in which they occur and globally.