One of the most destructive government programs is war.
The common usage of the term is reflected in its dictionary definition: "open armed conflict between countries or between factions within the same country".
How deadly is war? R. J. Rummel has placed the death toll for the wars of the twentieth century at 36 million. While this is significantly less than the 262 million killed by democide, it is still a huge toll. Beside this, war has caused much suffering and destruction of property.
How could this happen? Government has a near monopoly on force, so when its leaders decide to use that force to kill, it can be very deadly. Only government has the power to coerce and motivate people to kill that much.
The people who start wars are not responsible for their effects. They generally do not suffer personally from the decisions that they make. Soldiers and taxpayers suffer the consequences of their decisions. Someone outside the government who wants to kill faces the very real risk that his victim will defend himself with force. Government decision-makers are shielded from such consequences.
Ironically, wars are practically the only government programs that ever end, since their effects eventually become too obvious to ignore.
So what can be done to prevent war? Armed citizens can deter private criminals, so an armed citizenry could help to deter or repel an invasion. However, their effectiveness in preventing an invasion by a highly organized army would be limited.
Organized groups of armed citizens, or militias, could be more effective. The best example of effective militias is Switzerland, which deterred Nazi invasion during World War II, even when it was surrounded by Nazi-controlled territory. However, a militia is not foolproof, and it cannot defend a nation's interests abroad or at sea.
Thus a nation that wants to defend itself against aggression and deter war needs a military. A military needs to be funded, and government taxation appears to be the only way to do this. The more likely a government is to be successfully resisted, the less likely it will be to attack another country. Thus it is possible to achieve "peace through strength".
When should a nation go to war? This question has been addressed in Christian just war theory.
One well-publicized observation is that democracies do not go to war with each other. There are some cases on the margin, such as the American Civil War, that challenge this observation. But it appears to usually be true. It appears that this is because democracy imposes some measure of accountability on politicians, and war against another democracy cannot be politically justified.
War destroys lives and property. It lead to restrictions on freedom at home. It is usually less successful than its proponents envision. Still, it is sometimes necessary to protect a country. When fought, it should be for the realistic goal of defeating the enemy, not for utopian goals of nation-building and imposing democracy. This will minimize harm and maximize the chances of success.
War is a vivid example of the destructive power of government.