Military ranks

Robert Gates, the outgoing US defence secretary, recently used his valedictory address in Brussels to chide those countries that, in his words, "enjoy the benefits of Nato membership . . . but don't want to share the risks and the costs". Gates had in mind how just five of the 28 Nato allies - the US, Britain, France, Greece and Albania - now meet the informal commitment to spend at least 2 per cent of GDP on defence. Since the end of the cold war, the US share of Nato defence spending has risen from 50 per cent to 75 per cent. As the graph shows, the US is also the only Nato member to feature in the world's top ten military spenders (as a proportion of GDP). David Cameron is fond of boasting that the UK has the fourth-largest defence budget in the world (£33.8bn or 2.7 per cent of GDP) but this is true in cash terms only, a poor measure of a country's commitment to military spending.

A

The defence data, provided by the Stockholm International Peace Research Institute (Sipri), comes with several caveats. The figure for Saudi Arabia, for instance ($45.2bn, or 11.2 per cent), also includes spending on what is euphemistically described as "public order and safety". The figure for Israel ($13bn, or 6.3 per cent) does not include the $2.9bn that the country received in military aid from the US in 2010.

Nonetheless, the Sipri index, introduced in 1967, remains the most authoritative guide to defence spending. Global military expenditure in 2010 was $1.63trn, a real-terms increase of 1.3 per cent. This increase, however, was almost entirely due to the US, which accounted for $19.6bn of the $20.6bn rise.

In absolute terms, the US accounts for 43 per cent of the world total - six times its nearest rival, China (7.3 per cent).