The whole world needs to be worried about the wealth concentration in a few hands. Every measure of inequality across the world is indicating towards it and it has turn to be almost universal truth today by every institution Oxfam or others.
Rising inequality is cause of concern but such concentration and accumulation of wealth in few hands at the end day would undermine the democracy and democracy over time will turn into oligocracy in which only a few will remain important. Rest would not matter.
