Prediction is difficult, except retrospectively.
But what would be my prediction for the dominant world nation in 30 years?
(Assuming the same nations, and excluding the possibility of new colonies, e.g. European nations taken-over and run by other groups.)
On present trends and assuming there is no 'Great Awakening' of Christianity in the West (for which we are hopeful, but not optimistic)...
Here are the assumptions I am working from.
1. The nation would be one with a young and growing population of reasonable size.
(This rules out the West and East Asia and Russia - all the most internally-complex societies; which means that the dominant society in a generation's time would be a society that is currently of mid-range complexity.)
2. It would be Islamic, and ride the rising tide of Islamic demography.
(Because, before 25 years have elapsed, one in four people in the world will be Muslim. http://pewresearch.org/pubs/1872/muslim-population-projections-worldwide-fast-growth This rules out most places. )
3. It must want to be the dominant nation, and be psychologically-capable of becoming the dominant nation.
(This rules out quite a few other places; and is of course a further factor in eliminating The West.)
Turkey seems to fit the bill better than any other - as (I think) the only nation left-standing after applying my assumptions.
It has a biggish population, a large military, is increasingly devoutly Muslim, and apparently wants to be a world power. Again. Because of course Turkey has many centuries of Empire behind it - so Turkey's recent state of relative weakness is the historical anomaly not its dominance. And there is likely to be psychological readiness for the particular demands of being a world power.
So on current trends I would envisage Turkey as (again) becoming perhaps the most dominant world power in about a generation's time. Although not with a global reach, nor domination everywhere; because no-place will have a global reach by then - but perhaps more powerful than any other contender.