When a US warship steamed through the South China Sea the other day China protested and her neighbours applauded. Washington said it was upholding freedom of navigation in the face of Chinese land reclamation projects that are turning disputed rocks into artificial islands. Beijing warned against provocation from an outsider with no claims of its own in the region. The rest of us were reminded of the dismal determinism of Thucydides’s account of the Peloponnesian war.

The demonstration of US naval power — the ship sailed in waters deemed territorial by China — pointed up the multiple collisions of competing historical claims, geography and shifting power balances fuelling an East Asian arms race. Some say there are now as many submarines prowling the waters of the western Pacific as there once were in the north Atlantic. Vietnam, the Philippines, Taiwan and Malaysia also contest the “nine-dash line” that asserts Chinese suzerainty over the South China Sea. Tokyo and Beijing are locked in a separate dispute in the East China Sea.

Just before the guided missile destroyer USS Lassen set its course, I joined the serried senior ranks of the People’s Liberation Army at China’s annual international security conference in Beijing. I have never seen so many starred epaulettes.