War is, sadly, part and parcel of human history. As far as we can tell, humans have been at it for as long as our species has existed on this planet - and animals were in conflict before us. Some of the earliest evidence of warfare was unearthed in Kenya, where anthropologists uncovered remains of people who had died violently sometimes between 9,500 and 10,500 years ago - the earliest scientifically-dated evidence of organized human violence. War could be a consequence of our biology, or a completely human construct initiated and maintained by organized societies.
The triggers for war are pretty diverse but generally center around some common themes like the need for resources, conflicting ideas, expansion of territory, revenge for perceived wrongs, frustration with the status quo (i.e. revolution). The two major world wars of the 20th-century include some aspects of all of these, with the complication that WW1 was largely seen as an unsatisfactory end to the burning pressures between interested parties. This, according to some, laid the ground for WW2, and, to a certain extent, continued into the Cold War and beyond.
Mass Migration
Throughout most of human history, mass migration has been the result of, not the cause of conflict. The Hunnic invasions of the 5th Century being a good example. But some believe that the kind of mass migration we have seen over the last decade or so could set the scene for conflict in the not too distant future. The reason for them vary from civil wars to environmental disasters or economic desperation. And these issues are likely only going to get worse as populations rise.
Russia-Ukraine Conflict
Russia's invasion of Ukraine is a historical event and it's effects will likely ripple out for years to come. Countries across the globe are already rethinking their entire foreign policy, and that's just the beginning. Every government will be watching closely to see what unfolds in Ukraine and whether the global response to Russia is able to deter even greater escalation. It's worth remembering that we're only a week into this war and things are changing by the day. No one really knows how it will play out.
Taiwan's Issue
Taiwan is something of unfinished business for the Chinese Communist Party. After the conclusion of the Chinese Civil War in the 1940s, remnants of the defeated Kuomintang controlled Republic of China took refuge on the island. The People's Republic of China (PRC), to this day, considers Taiwan as part of China and does not recognize the legitimacy of the ROC. If China decides to invade the island, this could, trigger a chain of events that could escalate very quickly.
Water War
The world's population is around 8 billion today. This is set to grow to 10 billion by 2050. That's 2 billion more mouths to feed & water. While some are confident technological improvements and management strategies can handle it, others are concerned that this might reach a tipping point in which demand outstrips supply. If the pessimists are right, water and food shortages will likely not be taken lightly by much of the world's population. After all, food scarcity was one of the major triggers for the French Revolution.