" I cannot see how it could assist any state's cause to allow the world to see a man like Alan dying," Barbara Henning said, according to a message released by the UK Foreign Office. ISIS refers to itself as "the Islamic State."
I'll reply to the simpler question first. Cause here means ideas, goals, the general ideology of a state. The way a state sees itself in the future. The way a state sees a future world, changed through this state's efforts.
Barbara basically says that:
- She understands that the world has a wide variety of states. A state (a country) may have very radical long-term goals and very radical ideology (cause).
- But she doesn't understand how could the publicly displayed murder of a person help any state reach its long-term goals, promote its ideology, implement its plans ( = assist its cause).
The phrase how it could assist is not an idiom. The word it stands for "allowing the world to see a man like Alan dying". To rephrase,
I cannot see how allowing the world to see a man like Alan dying could assist any state's cause.