In a world united under one constitution it would seem that there would be one fundamental challenge, other than the myriad acute challenges of political power, and that would be vandalism in a world where blame for all behavioral failings is laid to bacteria. Such a world would be deprived of its current answer to vandalism--punishment. How could vandalism be prevented from spinning out of control and destroying civilization from within?
This is a problem no one has considered, because bacteria are deemed incapaable of intelligent behavior.
Here I am using the term vandalism to include all crime, up to and including terrorism.
Much depends on how well the argument that bacteria regulate all central nervous systems goes, and with which groups and individuals. That also will determine whether the world will ever unify under one constitution.
Much also depends on how much understanding of misfortune comes about, and what government decides is rightfully addressed, as a result of a successful argument about bacteria.
I see no reason why humans shouldn't seek a symbiotic steady-state with bacteria, something on the lines of what some insects have. If human leadership is able to understand the argument but the masses are not, as I suspect will be the case, then a serious schism will come about that will give serious power to those who understand, and a more stable environment for others. In a sense, everyone stands to gain significantly.