There are a number of factors. As somebody else has pointed out the technological means of disseminating the world news related to tensions and warfare have improved so much that it appears almost instantly in your living room. During the last world war the actuality of warfare appeared in your 'living room' but other bad news was largely suppressed to maintain morale.
The technological means of killing people and destroying property has advanced considerably and continues to do so. This coupled with the world population explosion and density probably means that there are more potential casualties and destruction of property and mass migrations.
As the world resources dwindle political power blocks will flex their muscles to exercise control over getting their 'share'.
As more and more people are forced to live in precarious geological zones e.g. lowland areas, tectonic areas, any natural disasters will create more casualties. Diseases will spread more quickly.
.... and that's just the good news.
Can I take it that you agree with the OP then?
I get the impression that tensions across the world are growing but then this has probably always been the case when empires have risen and fallen and other power structures have fought to fill the vacuum. The impression could arise from the competition between mass media outlets to outperform each other in public presentation. Also with the advent of the Internet it is difficult for secrecy to be maintained by those wishing to suppress negative news or those with an agenda to present disinformation. I suspect that as populations swell, it will become more and more difficult to control the masses that have they become critical.
...and, when tensions do grow things become polarized, as you suggest, and then things take off like a nuclear reaction.
Let's hope it doesn't become like Calhoun's rats:
" Using a variety of strains of rats and mice, he once more provided his populations with food, bedding, and shelter. With no predators and with exposure to disease kept at a minimum, Calhoun described his experimental universes as "rat utopia," "mouse paradise." With all their visible needs met, the animals bred rapidly. The only restriction Calhoun imposed on his population was of space--and as the population grew, this became increasingly problematic. As the pens heaved with animals, one of his assistants described rodent "utopia" as having become "hell."
Males became aggressive, some moving in groups, attacking females and the young. Mating behaviors were disrupted. Some males became exclusively homosexual. Others became pansexual and hypersexual, attempting to mount any rat they encountered. Mothers neglected their infants, first failing to construct proper nests, and then carelessly abandoning and even attacking their pups. In certain sections of the pens, infant mortality rose as high as 96%, the dead cannibalized by adults. Subordinate animals withdrew psychologically, surviving in a physical sense but at an immense psychological cost. They were the majority in the late phases of growth, existing as a vacant, huddled mass in the centre of the pens. Unable to breed, the population plummeted and did not recover. The crowded rodents had lost the ability to co-exist harmoniously, even after the population numbers once again fell to low levels. At a certain density, they had ceased to act like rats and mice, and the change was permanent. "