Should the UN control the world's military?

Civilised countries have a military for self protection and for the assistance of other nations that need protection. In some cases they are used preemtively to protect our interests from extremist govenments, but if the majority of the world agreed to allow full control of their military to belong to the UN and effectively a global military, primarily in a peacekeeping role, whose purpose would be to ensure that rogue states comply also. Ultimately, the removal of the armies from government power raises the question about whether a govenrment can hang on to power without a military or if there would be endless internal coups, however good government won't need it and rogue elements that attempt an overthrow could be dealt with by the the UN. Would it work to unite us by removing the tool of conflict? Is there a 'down side'? What are your views and alternatives?