The 'standard' attitude to group selection in mainstream evolutionary biology is that it is an explanation of last resort - which should only be invoked when the possibilities of organism-level selection (by 'selfish gene' mechanisms) have been exhausted.
But from a complex systems theory perspective group selection should be investigated, as the first line of enquiry, whenever certain conditions prevail - as follows:
A complex system can be identified when there is a concentrated and lasting network of communication-interaction between entities - when we find such a situation in biology (or elsewhere), then we may assume that we have an entity which may be selected.
For example, such dense communication-interactions may be identified within a single cell, between the cells of a multi-cellular organism, or between the organisms in social organisms.
Therefore each relatively discrete human group (of whatever size) - where there is a much greater density of communications within that human groupings than exists between such human groupings - is a situation where group selection would be expected.
Group selection was therefore usual through much of human history when there were groups that had little or no communication-interaction between them (for example, when geographically separated, or separated by any other 'barrier').
But the strength of group selection is reduced by any significant increase of communication-interaction between groups.
Therefore (all else being equal) 'globalization' is expected to reduce the strength of group selection for whatever groups are included; since globalization refers to a significant increase in the communication-interaction between groups.
The modern 'globalized' world is therefore a world in which levels of local and national group selection has been weakened; and the most modern parts of the world are those in which group selection has most been weakened for longest.
In such a situation, it can be assumed that individual level selection will have been weakening group selected traits for several generations - with the effect of diminishing the instinctual basis of social cohesion.
In summary; group selection is not so much a consequence of competition between groups, as it is an intrinsic aspect of dense communication-interactions within groups in a situation with little communication-interaction between groups.
Reference - see Appendix of: http://www.hedweb.com/bgcharlton/modernization-imperative.html