China is at least integrated into the world economy so much that they won't want to cause ructions (though the whole world was pre-WWI)...
Russia though is a beast with a chip on its shoulder, which won't take the loss of Empire as well as the UK managed.
BelArg - Eastern Europe works for the best stage at which missiles launched from Iran would be most accurately shot down. Russian missiles would not only be more Northerly, but are at a quite different boost stage to be shot at from there - same issue with Turkey in being too close proximity to Iran.