It is likely that Romans made no distinction between today's
terms integration and assimilation. They did everything that was
necessary for the expansion of the Roman empire and worked from
experience. Due to the communication lag between Rome and
conquerors in distant, marginal territories, there had to exist
directives/guidelines on how to deal with newly conquered
cultures/tribes. While the Romans adopted a lot of foreign
culture as well (e.g. Greek philosophy, mythology), they likely
didn't allow conquered tribes to practice their
religion/language any more (?). That's probably the rough border
line between integration/assimilation compared to today's
meanings. Maybe they even married foreign women and killed
foreign male adults/children to "speed up" cultural
assimilation. What known and/or documented procedures did
conquerors/military tribunes conduct to assimilate foreign
cultures in the best way? What was "officially" prescribed by
the Roman senate and philosophy?