Harry Turtledove's Worldwar series had some interesting thoughts on how the presence of large oceans and family groups causes humanity to be better at war than a technologically superior alien species:
"One of the major aspects of the Race's society is that technological progress proceeds very slowly, on the scale of thousands of years. Their original unmanned probe that surveyed Earth a thousand years ago found only a medieval civilization of armored knights on horseback, but the Race was astonished that 20th century Earth had reached an industrial technology level, with radios and mechanized warfare. As the attempt to conquer Earth progressed, the Race was also horrified and confused that Earth nations could develop new tank models, from design phase to mass-production, in less than two years.
The Race speculates that the reason for this vast difference in the rate of technological development is partially historical, partially biological. Because the Race's homeworld didn't have large oceans, it was politically unified very early in its history. In contrast, Earth's large oceans encouraged its political division among rival nation-states. The result is that the Race does not possess the same history of constant, endemic warfare that Earth does. Such warfare fueled technological arms races, benefiting the human nations that were able to develop better weapons as quickly as possible. The biological aspect that the Race considers is that unlike the Race, human society is centered around nuclear families. This in turn led to political organization into clan-groups, and ultimately along territorial lines, fueling the competition between rival nations. In contrast, because the Race doesn't develop nuclear families, competition in the Race is along generational gaps between age groups, not clan groups."
