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China and India: two massive countries with huge populations that share a very long border but are not politically or culturally aligned. It wouldn't be surprising if these two giants had fought each other in several wars, but in fact, apart from one month-long battle in 1962, they never have. Why? Because between them is the highest mountain range in the world, and it is practically impossible to advance large military columns through or over the Himalayas. As technology becomes more sophisticated, of course, ways are emerging of overcoming this obstacle, but the physical barrier remains a deterrent, and so both countries focus their foreign policy on other regions while keeping a wary eye on each other.

On 3 June 1947 the announcement was made in the House of Commons: the British would withdraw - India was to be partitioned into the two independent dominions of India and Pakistan. Seventy-three days later, on 15 August, they were all but gone.

There are issues which cause friction, chief among them Tibet, the highest region on earth. As previously discussed, China wanted Tibet, both to prevent India from having it, and - almost as bad in Beijing's view - to prevent an independent Tibet allowing India to base military forces there, thus giving them the commanding heights.

Nor would Pakistan be considered a threat to India had it not mastered the technology of developing nuclear weapons in the decades following the partition of the region in 1947.

Britain is the third-largest investor in India, and many of the British firms that operate there, such as JCB, see no point in being in the EU. India, for its part, is the third-largest investor in the UK, owning more here than in the other twenty-seven members of the EU combined.

The area within our frame, despite being relatively flat, has always been too large and diverse to have strong central rule. Even the British colonial overlords, with their famed bureaucracy and connecting rail system, allowed regional autonomy and indeed used it to play local leaders off against each other. The linguistic and cultural diversity is partially due to the differences in climate - for example, the freezing north of the Himalayas in contrast to the jungles of the south - but it is also because of the subcontinent's rivers and religions.

As for India, it can multi-task - indeed it has to, given that it has more to think about than only Pakistan, even if it is the number one foreign policy priority for New Delhi. Having a hostile nuclear-armed state next door is bound to focus the mind, but India also has to concentrate on managing 1.3 billion people whilst simultaneously emerging as a potential world power.