There is also an intrinsic link between inter-group aggression, and intra-group cohesion. 
Inter-group
"Between-population differences in lethal aggression may also be owing to differences in ecological conditions, where higher and more predictable food availability and distribution are associated with reduced intragroup feeding competition, allowing for larger mixed-sex parties and thus more equal balance of power during IGEs. This hypothesis was also suggested for the absence of intergroup lethal raiding in bonobos. However, systematic comparative methodological approaches in assessing food availability, distribution and predictability across sites would be necessary to test this hypothesis."
It's bee
It has also been suggested that the variation in intergroup violence is itself driven by the variation in intra-group cohesion which is discussed below.

Intra-group dynamics 

Social cohesion is variable in chimpanzees groups, as their fission-fusion dynamics often lead to larger groups being split into smaller sub-groups and dyads throughout the day \cite{Couzin2009}.
The impact of intergroup violence on intra-group cohesion is well studied, particularly in chimpanzees where cooperative behaviour between non-kin individuals is seen on a group level (collective hunting and terriroty defence) all the way down to a dyadic level. 
The ecological constraints model posits a relationship between group size, territory size and food availability (however not necessarily a relationship between any two), as food availability decreases for existing populations and as  - Whether these changes end up reducing group size or territory size long term remains to be seen. 
Increased seasonality in food availability in chimpanzees has been associated with increased levels on infanticide and decreased female sociality \cite{Doran_2002}
The shared experience of inter-group conflict

Interspecies conflict

As the climate crisis and it's outcomes degrades access to fundamental resources, such as sources of water and food the available niche space for all megafauna, including humans, shrinks \cite{Virah_Sawmy_2010}. Species that were previously able to co-exist in the same area begin to come into competition with each other for resources that were previously did not constrain population size. \cite{G_mez_2016}. Most notably this is likely to increase human-wildlife conflict as humans are most able to defend and protect limited resources, and changes to biodiversity in natural habitats limits great ape nutritional options from non-Anthropogenic sources \cite{Kamgang_2021}. However this resource limitation can also lead to interspecies violence between non-human great apes. A recent example of interspecies violence occurred in Gabon, where a group of male chimpanzees patrolling their territory's perimeter hunted and killed an infant gorilla \cite{Southern_2021}. This event
However notably there is a large dietary overlap between these individuals which is predicted to increase with time. 
evel of habituation to human observers of communities that are neighbouring to the studied habituated chimpanzee communities
may also explain some of the observed differences in rates of lethal interactions across sites. It is expected that habituated communities with non-habituated neighbours may have a competitive advantage during IGEs, as the fear of humans may disrupt cooperative response of non-habituated communities.