Why is the world not acting/reacting to these actions?

The problem is "the world" already doesn't view ISIS as an entity that can be held accountable. Furthermore, their actions are no longer surprising. This is pretty low attention compared with atrocities they have already committed. By not caring about what the world thinks and international public opinion, they are no longer bound by them; something the US military could not afford to do.

SSG, why should we? If those in the country affected don't care, will not rise up to fight, or think it's better to run or even join, why should we care? It's just like with the Taliban when I was in the Stan; out of a village with a few hundred, there might be 10 Taliban maybe? Yet those 10 would wreak havoc in the village and surrounding areas and no one would group together to stop them. I'll bend over backwards to help anyone in need, but you have to want it as much as I want to help you. Some of these affected folks just don't.

There has been condemnation statements from many countries. But the whole world is going PC following our lead. The UN is totally noneffective and is even giving nukes to Iran. But that's a different subject, or is it....