I definitely think if an organization such as the UN Assembly worked on treaties for global truces and global cease fires, wars would be reduced around the planet. I think that efforts to take diplomatic approaches are always the most important. But also taking a proactive approach to peace and truces is significant as well.
No, the likelihood of war would not be reduced if the UN Assembly worked on treaties for global truces and global cease fires, because at the end of the day, there are countries around the world that just have large differences. There are things that we cannot compromise on, and there are things upon which the entire world will never agree.
There will always be criminals in this planet, and in that case there will always be corruption. This corruption could be at the national, local, and most often international level. There will always be someone breaking the law on a global scale and making millions angry, thus is the life.
The United Nations has long been seen as an generally ineffective organization in recent years, I believe many countries would ignore and true or cease fire agreed upon at the United Nations and in general I don't believe the United Nations should be in the business of brokering peace agreements and cease fires.
I do not believe the likelihood of war would be reduced if the UN Assembly worked on treaties for global truces and global cease fires. Treaties are simply pieces of paper, they don't make tensions disappear. Furthermore, I think the UN does work on these principals already, when they do come up.