Overview
The core nature of the world system is the artificial propping up of money and debt, with state power, to allow the extraction of wealth by the political and financial elites from the rest of society.
Objectively speaking, war and terrorism are often caused by the ill-effects of this system, but also play a significant role to support the system. (The latter may seem surprising at first glance.) This is not to excuse any of the truly evil characters for their direct parts in these horrendous occurrances, but to explore the intriguing interplay between the nature of the system and these events.
The System's Role in Creating War and Terrorism
When the artificially over-valued financial assets eventually crash (which seems inevitable, both from history, and given the incentives for members of the elites to destabilize their own system,) misery afflicts entire economies and societies, and none more so than in vulnerable and peripheral countries.
The severity of the Great Depression in Germany (a country very much at the receiving end of global monetary and financial power at the time) led to the rise of the Nazis, which led to the war. The long-running economic deprivation of large parts of the Middle East is objectively brewing terrorism. It's worth noting that the world system is very good at keeping rich countries rich, and poor countries poor, beyond the natural "real-economy" factors that separate the two. The "exorbitant privilege" of reserve currencies and "uphill capital flows" starve poor countries of investment and actually transfer wealth from poor to rich countries, in a process that's not dissimilar to the way Western elites take wealth from the rest of their populations. (I hope to have time to explain this in more detail in future.)
How War and Terrorism Support the System, Or Not
The major benefit that war and terrorism bring to the reigning global hegemon (which must be a geopolitical, military, as well as financial leader in modern times) is that, after the hegemon's victory, it's in such a strong position, relative to other countries, that it has enough power to strengthen financial repression and thereby stabilize the inherently unstable world sytem for the time being. This happened in favor of the US after both world wars. The gold standard took a major step to becoming a "dollar standard" in both cases. Britain's victory in the Napoleonic wars (decisively taking France out of the running for global hegemony) paved the way for sterling to be the global paper reserve currency. After the 9/11 attacks, the US was also able to expand electronic surveillance, which has been exposed by Edward Snowden to include economic, as well as counter-terrorist, eavesdropping.
But this support is a double-edged sword. Fighting wars and terrorism forces the global hegemon to increase financial leverage (typically by borrowing more money) and so helps destabilize its system. Worse, any conflict tends to upset the delicate international network of monetary and financial support that the hegemon has carefully arranged for stability. (For example, the US invasion of Iraq in 2003 was stressful to the US-Saudi relationship that was critical to the "petrodollar" system.)
The Crux of the Matter
So, fighting war and terrorism objectively becomes, on balance, beneficial to the system only when the forces that it battles have become so unpopular that most of the world is united against it. (Or, the hegemon is otherwise assured of victory in a great battle.) The global hegemon would enjoy a better chance of winning. Plus, after a truly cataclysmic event, it will have an easier task remaking the world system to its liking. Also, any financial "irregularities" associated with this change can easily be blamed on the great event.
This may be why the US- and dollar-dominated system gained strength after both world wars, but the Vietnam and Iraq wars contributed in a major way to financial instability and devaluations of the dollar against gold.
From a totally cold-blooded point of view, then, the elites' logic is overwhelmingly in favor of waiting and letting evil forces grow stronger. I am speculating this was why Hitler was appeased through his aggression in the Rhineland, Austria, the Sudetenland and the rest of Czechoslovakia, and why the US can't seem really to go after ISIS.
We shouldn't automatically assume the elites cynically allow the enemy to grow strong under the above logic. It's possible that they simply understand the weaknesses of their overall system enough that they take a more cautious approach than the public might assume they should. (Remember the core of the modern system is financial leverage (with its benefits for the elites,) which is unstable by nature.)
But either way, the nature of the system is objectively fostering the atrocities committed by the enemy, both by bringing them on in the first place, and by being powerless to stop them early.
Gone are the days when wars were fought by major European powers to grab land, colonial labor, other real economic resources, and thus room for more financial leverage. The calculus was more in favor of war then. The world simply won't allow daylight theft today, and I suppose this is progress. Instead of driving the Western elites themselves to war, the incentives of the system today drive, indirectly, the likes of the Nazis, the Soviets, al Qaeda, and ISIS to create conflict.
This is not to blame war and terrorism on the Western elites, but to supply some hints that can hopefully be used by those with good historical knowledge to build a more complete picture of the meanings of war and terrorism. No one wants these terrible things to happen, and understanding them further will hopefully help us clean out both the direct and indirect factors that make them a fact of life to this day.