They want a base in the Middle East and they have many reasons to be there, oil being one of them, they actually get it from there. As Trump says (today), the US does not have any need for their oil, so in that sense China has more reason to be there.

Mutually Assured Destruction has worked for 75 years, China is aggressively expanding their stockpiles. Would the US or Israel risk a war with China over Iran if they get the assurances from the Chinese they will keep Iran on a tight leash?

> Why would China agree to that?

Ultimately the aim to displace the US as the world hegemon. Having bases across the world is what hegemons do.