I think it is possible for world peace. Our world is full of hate, violence and sadness, and people see it. It is in our nature to want peace. We crave happiness and joy, even when we are angry or sad. Every huge act, every big change, started with one little thought, one little action. If one country decided they wanted peace, how can you look at them and want war? Its like in our everyday lives, one person steps up and then others join in, feeling braver to stand up for themselves. One country wants peace, another steps up and joins them. It may take a while, but sooner or later it could end up being continents wanting peace. It's all about excepting each other's differences, respecting each other's beliefs and decisions.
The more people could step up to be brave and fight for their country, the more people would die and there would be revenge. Also, you said that there was hate in thhe world. Plus, even though you look them in the face and tell them that you don't want war, presidents and dictators would rather have war than give it up and not get revenge on the other country.
Yes, some countries or people want power and become bullies and murderers like Adolf Hitler, but does that mean you should give up hope and resist yourself into being bullied, forced to defend your self, or even hide? No, there will always be hope of peace. There may always be people that want power, but if there was enough peace in this world, people would agree when they look back at all the hate, sadness and wars, that the peace should not be disturbed. You said that when your people die, you want revenge. Have you ever thought that in wars, we are killing other people? People of our own genus? For peace to exist there must be sympathy and admittance to your own faults. We have killed others just as they have killed us. All are to blame.
Greed and hate are apart of this world, you are right about that. But without greed and hate, we would not know how to find happiness, kindness, joy, and ultimately, peace. We would not be able to see our mistakes and learn from them. Without greed and hate we may not have light and darkness, but everyone knows, light will always prevail, light will always win. It is against our nature otherwise. Peace will be hard to achieve, but it is not impossible. Nothings impossible.