System of rule where romans gave full citizenship to some conquered peoples

Roman Confederation, is the right answer.

Explanation:

The phrase "Roman confederation" applies to the Roman way of administering Italy throughout the Republic. This system was created by the Romans to manage their new conquering. However, the Romans, under this system, awarded complete citizenship to some peoples. These people could cast their vote and participate in politics. Moreover, under this system, they were treated the same as the other citizen of Rome.

The system of Roman government, had a social organization which covered from the natives to the slaves and foreigners, nevertheless by means of the edict of Carcalla in the year 202, the citizenship was granted even to the conquered towns, this reform made the Emperor Carcalla, with the purpose of everyone paying their taxes.