1. I don't speak of the police to be disbanded, that would be foolish, but of current national militaries to be disbanded ? Police are necessary including armed police and even in the current circumstances don't police act against armed criminals to an extent ?
2. In a circumstance where the socio-economic system has been removed of Capitalism everywhere on Earth and there no longer are traditional Capitalist socio-economic classes ( rich, middle, poor ) and every citizen of Earth is potentially able to access all the goods and services from everywhere on an equal basis either free or paid through an evolved money system and no longer needs to participate in a dog-eat-dog work environment to "pay for the bills" as has been traditional in Capitalist systems currently and land is removed from private possession to become managed by people's land committees on behalf of the masses then why would that person do socio-economic systems like theft, fraud, money-related murders, muggings, gang formation etc ? The only criminals who will operate in the changed system will be sociopaths and psychopaths and will be dealt with extreme prejudice by the police. In a nation-abolished Earth circumstance the polices of cities and regions will collaborate to eliminate any remaining criminals. In the USSR murder was considered a Capitalist crime because of the above reasons and because of the progressed social system there - democratic equality within the family and generally outside.
3. The one to apply the suggestions from the masses of Earth would be a named UNO called perhaps General People's Congress for Earth. Please read my linked 'political system' thread as to how.
Such were the ultimate intentions of the USSR, the Libyan Jamahiriya, Japanese Red Army, German Red Army Faction, Carlos the Jackal, Che Guevara etc - World revolution.
Laal Salaam !