Peace is essentially the absence of conflict and strife while at the same time being the presence of harmony. Since conflict can occur on many levels of life and since harmony can be present in many classes of situations, peace may exist and not exist simultaneously in any one person's life, society, culture, government, or world at any one time. In other words, personal peace is very different from and not necessarily related to or dependent upon world peace or social peace (though personal peace and domestic peace are much, much more tightly interwound).
Peace begins with understanding. This is true both of fighting and inner peace. If you don't understand yourself, you cannot have inner peace. If you don't understand others, and others don't understand you, you cannot have peace with others.
Indeed, "peace" can be interpreted or defined in many different ways.
Inner peace reflects ones acceptance of the conditions in which one finds oneself. Inner peace suggests no conflict about actions or motives, no striving to change circumstances or people because there is no discord related to the situation at hand.
Are you talking about inner peace or are you talking about peace between nations?
In either case, one important question to think about is whether peace is a negative concept (whether it's defined as the absence of war or the absence of stress) or a more positive one (defined as the presence of good will toward other nations or the presence of positive happiness in the person).
With nations, I'll say peace is the absence of war. But in people, I'd say that it's the presence of a true sense of deep happiness or contentment.
We can say that peace begins with one person taking responsibility for his or her own well-being, state of mind, etc. From there it can spread, but without a beginning like this it will be a negatively defined concept - a lack of something - not a positive one.
There are so many possible answers. In my opinion, peace begins when there is a great hunger and desire for it. It starts with individuals and then it grows to encompass a larger group. Peace can only be sustain in a fallen world through acts of love and forgiveness. Unfortunately, it is hard to cultivate these qualities. Perhaps this is why there is the lack of peace in our world.
I think this is actually a highly complex question, as peace is something that can be defined in many different ways. You need to think about what kind of peace it is you are actually talking about. If you define peace in its purest sense, then perhaps #2 is right in thinking of peace as something that starts in our heart. However, often peace is a state that is adopted out of convenience or pressure.
I will choose a corny answer and say that peace begins in each individual human heart -- that if there is a desire for peace within oneself and with others, such peace is at least a possibility. Without an individual desire for peace of mind, such peace seems unattainable, and without a widespread desire for peace between persons, such peace seems unlikely.
Peace means "No to war."
No to war with the self.
No to war with others.
No to war in all parts of the world.