In geopolitics, some of the most consequential real estate is not vast — it is narrow. A river, a valley, a strait, a strip of land twenty kilometres wide: places where geography squeezes movement into a single line, and whoever controls that line controls what can pass. Tim Marshall calls these pinch-lines. They are how small states punch above their weight, and how great powers acquire disproportionate leverage over their neighbours. This chapter walks through three of them: the Indus that keeps Pakistan alive, the Siliguri corridor that stitches India together, and the Zangezur strip between the two halves of Azerbaijan.
The Indus rises in Tibet, curves through the slice of Kashmir that India administers, and then flows the length of Pakistan to the Arabian Sea. Every major Pakistani river is part of the Indus system, and Pakistani agriculture depends on it almost totally. The 1960 Indus Waters Treaty, brokered by the World Bank, split the six tributaries between the two countries and has survived three wars — but the underlying fact remains. India sits upstream. If New Delhi ever chose to weaponise that position through large-scale damming, Pakistan's rivers would begin to dry up. This is a geopolitical fact that no diplomatic language can erase, and it is why every crisis between the two countries eventually circles back to Kashmir and to water.
Look at north-east India and you find a piece of geography that ought to keep Indian planners awake. The Siliguri corridor — the 'Chicken's Neck' — is a strip of Indian territory only about 22 km wide at its narrowest, wedged between Nepal, Bangladesh, Bhutan and China. Through it runs the road, the rail and effectively the political connection between the Indian heartland and the seven north-eastern states. Cut the neck and roughly 45 million Indians are geographically severed from the rest of the country. This is why India watches every Chinese road, bridge and outpost in Bhutan with such intensity, and why the 2017 Doklam standoff — a bulldozer dispute on a Bhutanese plateau nobody in Europe had heard of — was treated in New Delhi as a first-order strategic event.
Now look at the South Caucasus. Azerbaijan is a country in two pieces: the main body around Baku, and a smaller exclave — Nakhchivan — cut off from it by a slice of Armenia called Zangezur. To move between the two halves of your own country, an Azerbaijani has to cross Armenian territory, which for thirty years has meant not moving between them at all. In 2023, after two wars, Azerbaijan re-took the enclave of Nagorno-Karabakh, and in 2025 a US-brokered agreement opened what the White House called the 'Trump corridor' — a transit route through Zangezur linking Baku directly to Nakhchivan and onwards to Turkey. That corridor is more than a road. It is the missing overland link between the Caspian and Europe, bypassing both Russia and Iran, and it turns Azerbaijan from a landlocked exporter into a hinge state in Eurasian trade.
Once you know what to look for, pinch-lines are everywhere. Georgia's Roki tunnel. Suez. The Bosphorus. The GIUK gap in the North Atlantic. The Strait of Hormuz. The Panama Canal. Ukraine's Kerch Strait. Each one turns a modest piece of geography into a lever, and the states that hold the lever gain influence out of all proportion to their size. Whenever you see a border dispute that seems disproportionate to what is actually at stake, look for the pinch-line — nine times out of ten, that is what the fight is really about.