In 1890, an American naval officer named Alfred Thayer Mahan, lecturing at the new Naval War College, published The Influence of Sea Power Upon History, arguing that control of the sea — through merchant fleets, a chain of coaling stations and bases, and a concentrated battle-fleet able to crush any rival in a single decisive engagement — had been the decisive factor in the rise of every great commercial empire from Athens to the British. The book was devoured in Berlin, Tokyo, and Washington. It armed Tirpitz's case for the German naval buildup that triggered the Anglo-German rivalry of the 1900s, it shaped the Imperial Japanese Navy's pursuit of one climactic fleet battle right up to 1941, and it drove the American expansion that produced the world's first true blue-water navy. Mahan's book changed the geography of the twentieth century.
The sea-power vs. land-power distinction is among the oldest in geopolitical thought, with Thucydides on maritime Athens against continental Sparta as the canonical original. Sea powers — Athens, Venice, the Dutch Republic, Britain, the post-1898 United States — share recurring features: commercial orientation, openness to migration and ideas, federal or republican institutions, dependence on trade routes, and acute vulnerability to blockade. Land powers — Achaemenid Persia, Rome (mostly), the Mongols, France, Germany, Russia, China — tend toward the opposite cluster: agrarian or extractive economies, centralised bureaucratic administration, large standing armies, lighter reliance on overseas trade, and vulnerability to invasion across open frontiers. Wars between the two types tend to become protracted attritional contests: the sea power blockades, isolates, and bankrolls coalitions while staying out of the decisive land battle, and the land power tries to seize a coastline or knock out the sea power's continental ally before the financial squeeze tells. The Anglo-French wars (1689–1815), the two world wars (Britain and the US against Germany), and the Cold War (the US against the USSR) all fit the pattern. The typical outcome — the sea power prevails because trade-funded credit and access to global resources let it outlast the land power — has held more often than not, though Athens' destruction at Sparta's hands is the standing reminder that it is a tendency, not a law.
The contemporary US-China rivalry maps cleanly onto the sea-power-vs-land-power template: the US is a Pacific naval power running a Mahan-derived doctrine of forward-deployed carrier groups and a string of overseas bases, while China is a continental state building a Mahanian battle-fleet — already the world's largest by hull count — and the Belt and Road overland network at the same time. Whether China can become both a land and a sea power at once, something only the United States has ever sustainably managed and which exhausted every European power that tried, is one of the most consequential strategic questions of the century — and one Beijing is spending heavily to answer in the affirmative.