George Friedman explains why China is not a contender:
Han China is surrounded by four buffer states, Manchuria, Inner Mongolia, Xinjiang and Tibet. Without these buffers, the borders of China move inward and China becomes vulnerable. With these four buffers in place, China is secure — but as a landlocked island, bounded by mountainous jungle, the Himalayas, the steppes of central Asia and the Siberian wasteland. China is blocked in all directions but the sea.The vast majority of China’s population lives within a thousand miles of the Pacific coast. Beyond this line, water supply will not support large populations. Most industrial development has taken place within a hundred miles of the coast. Consider the following numbers, culled from official Chinese statistics. About 65 million Chinese people live in households with more than $20,000 a year in income. Around 165 million make between $2,000 and $20,000 a year. Most of these live within 100 miles of the coast. About 400 million Chinese have household incomes between $1,000 and $2,000 a year, while about 670 million have household incomes of less than $1,000 a year. China is a land of extra ordinary poverty. Mao made the Long March to raise an army of desperate peasants to rectify this sort of extreme imbalance. The imbalance is there again, a volcano beneath the current regime.
China would have to triple the size of its economy — and the US would have to stand still — if China were to pull even with the US in GDP. Militarily, China is impotent. Its army is a domestic security force, its ability to project power blocked by natural barriers. Its navy exists mostly on paper and could not possibly pose a serious threat to the US. Casual assertions of China surpassing the US geopolitically ignore fundamental, overwhelming realities. China could conceivably overcome its problems, but it would require most of the century to overcome problems of this magnitude.