What would be a rational reason for Western countries to unethically intervene in the Middle East following a total economic collapse?
I'm writing a story where Middle Eastern countries descend into political and social anarchy as a result of the collapse of their crude oil-based economy. I’m referring specifically to those countries dependent on crude oil production to sustain their economies. Let’s assume for argument’s sake that Western countries are unaffected (they have other crude oil sources or other sources of fuel).
If the oil economy collapsed, whether due to an imposed embargo or their own decision to stop providing oil in response to Western sanctions, this would result in social and political anarchy in the Middle East. I'm particularly interested in how they could descend into anarchy that is serious enough to warrant foreign intervention.
In my story, the Western world feels that the situation in the Middle East is of sufficient threat to other countries that they could justify intervention using unethical means. They send undercover spies to the Middle East to "put a method to the madness" - not to restore civilization, but to confine the danger to the Middle East. They set up a sort of dystopia in which sanctioned killing is allowed. The story is set well into this dystopia, so the anarchy is just the backstory.
I'm going to assume that an economic collapse would result in insufficient resources, starvation, warring sects, use of nuclear/chemical warfare, etc. that lead to anarchy in the Middle East. At what point would the Mid-East pose a significant enough risk that the Western world would feel compelled to act?
I'm interested in answers that either (a) provide historical examples of how economic collapse led to anarchy extreme enough to warrant foreign intervention (and describe the foreign intervention that took place), or (b) provide a justification for a foreign country taking questionable steps to stop an anarchy from spiraling out of control.