How do you think it will come to be?

I personally think some strain of anti-biotic resistant infectious disease will surface and spread around like the Black Plague and wipe out a good portion of the Worlds population, which will have to be eradicated by disposing of anyone/thing infected meaning towns and cities quarantined and bombed, and tensions between countries will be strained by the stress this puts on the world and by other countries pushing 3rd world countries to do the same and with large areas of land once inhabitied by citizens of some countries being empty smaller/bigger countries will try to expand and take over those areas leading to an all out fight for power.
The way civilization has been collapsing and becoming stupider and stupider World leaders will become less rational as the years go by and the chances of war will be great no matter what.