Let's look at an example. Say I get food poisoning from some bad oysters that I ate last night at a restaurant. The most obvious cause would be the oysters themselves, or perhaps the bacteria in them; after all, if they hadn't been contaminated, then I wouldn't have gotten sick. That's how our minds work most of the time: we identify the closest and largest factor prior to an event taking place, then assign causality or blame to it. "If you hadn't called me when I was driving, then I would never have gotten into the accident!"
But what if the main reason that I visited the restaurant was because my coworker suggested it? Otherwise I would never have chosen that restaurant. Or say that same coworker told me, "You have to try the oysters at..." Obviously I wouldn't have gotten food poisoning from those oysters if I didn't order them from the menu, let alone if I had dined elsewhere. So aren't those two factors just as responsible for my getting food poisoning as the tainted oysters themselves?
Or say that the oysters went bad because the delivery truck's freezer broke down en route to the restaurant, which perhaps was the result of the truck company's financial inability to get the refrigeration system annually repaired. And so on and so on. Remove one of these conditions and the causal chain dissolves.
Which is why I can't stand the reductive "Everything happens for a reason" logic.
Everything happens because of a multitude of reasons.
34 American soldiers in Iraq are suffering from traumatic brain injuries from the Iranian airstrike a week ago. The Iranian response was a retaliation for the U.S.'s assassination of General Soleimani. So is President Trump responsible for these U.S. soldiers' injuries? Yes and no, in the same way as my friend's restaurant suggestion or the truck's broken freezer are integral conditions for my food poisoning.
Decades of U.S. foreign policy in the Middle East contributed to the political climate that allowed Soleimani and the Iranian regime to flourish. Every event interacts with every other one to produce an intricately woven tapestry of exchanges and counter responses. This inter-conditionality forms the heart of Buddhist thought and ethics, which one might argue are two words for the same thing.
Every choice we make echoes throughout the amphitheater of history. This knowledge can paralyze us with worry, for fear that any one of our actions could wreak or catastrophe. Or it can inform our actions so that we respond with wisdom and compassion in order to--as the Dalai Lama so beautifully and succinctly puts it--"Do as little harm as possible."
Image borrowed from: https://www.thoughtco.com/definition-of-chain-reaction-604899