The US will face a multitude of threats in the next 20-30 years but I think these three are on top of the list: (1) Islam: Not just rogue regimes like Syria and Iran but countries like Saudi Arabia and Egypt whose rulers are currently allied to the US but are ripe for a revolution. Perhaps even an Islamic revolution. Islam is in a major power struggle with the West and in my opinion, it could very prevail in this power struggle, although this will require a reforming and re-defining the religion for the 21st century. (2) China : China will compete with the US both economically and militarily. (3) India: This is another emerging power house. Although a bit behind China, it is likely to catch up and has the potential to surpass China. India will compete with the US for brainpower and given it's cost advantages will give the US a run for its money.