What it is: Generally, making up one's mind what course of action to take. In politics and other group activities, deciding on other people's behalf (with or without consultation) on a course of action.
What it means: Most human beings spend most of their waking hours making decisions. These may be small (moving out of someone's way) or large (moving to a different country). Human lives are a journey along paths that constantly divide, and we constantly have to choose which one to follow. We are also affected by other people's decisions. In local social groups - family, school, workplace, neighbourhood - decisions are made by people who lead. In regions and nations, it is governments (or the leaders of governments) that make the decisions affecting everybody. Because decision-making on a large scale is very complicated, people have devised decision-making processes: ways of getting and organising the information and situations that are necessary to make a decision. They try to cater for the possibility that some information may not be available, or that situations may change, or that there are risks to be wary of. But in reality, no standardised 'one-size-fits-all' decision-making process, anywhere, can be completely relied on to be fair: every case is different, and the future is unpredictable. What is more, some decision-makers may not be good at the job, or are interested only in their own futures. Things can go badly wrong. And when it comes to making decisions about war the risks are even greater. War (of any kind) always makes situations much more unstable, uncertain and unfair. The minds of people making decisions under stress usually function less well: when anxious, anyone can miss or misunderstand things and generally think less clearly. And that's only the leaders. What about the people doing the fighting?
Think about it: The history of the attack on Iraq in 2003 is full of examples of the pitfalls that decision-making processes nearly always meet. It's recent history, and it should be easy to find out about some of those examples. But it's always helpful to start with first-hand experiences: look at a decision-making process in the family or at school/work - especially one in which people (including you?) were under pressure of some kind.