Maritime empires eventually figured out that negotiating common rules for interaction was far more wealth producing than hanging on to hostile territories.

From Interview: Sarah C. Paine, A scholar of the 20th century explains the conflicts of the 21st by Noah Smith.  Where she sticks to her specialty, the history of the global economic order, she is very interesting.  Where she strays into contemporary domestic politics, she is just another academic opinion without the weight of expertise.  

I liked her summary model which maps to mine and which, for me, center the modern era on the accomplishments of Portugal and Henry the Navigator's captains as they opened up the sea lanes to all the world around 1500.  

A maritime power can, if necessary, defend itself primarily by sea, while a continental power cannot. This relates to geography: an island power like Britain can be invaded only by crossing the sea, whereas France, which also has a long coast facing the open ocean, has an equally long border facing Germany and the Low Countries. Both France and Germany have repeatedly invaded across that border and so require armies to defend it. Regardless of whether they buy large navies, their geographic positions are continental because of this landward vulnerability. 

Historically, the great civilizations of Eurasia were all continental empires. Maritime empires came later. The former focused on expansion into contiguous territories, while the latter focused on the expansion of trade. For the latter the territory was secondary to the trade—they took territories that produced the products traded or that served as bases en route to the trade. Maritime empires, such as the Dutch Republic, were interested in maintaining a system of universal international laws so that all could trade in safety. Hugo Grotius, the founding father of international law, was a citizen of the Dutch Republic. Continental empires focused on carving the world up into spheres of influence, each a legal world unto itself, and often fighting to expand at each other’s expense. 

The Industrial Revolution upended empires of both types by producing compounded growth. Maritime empires, already focused on trade, were far better positioned to adapt to this change than were continental empires bent on dominating territory. Moreover the advent of nationalism that gradually spread globally, starting in revolutionary France and the Napoleonic Wars, made the costs of empire unsustainable as dominated peoples resisted. Maritime empires eventually figured out that negotiating common rules for interaction was far more wealth producing than hanging on to hostile territories. 

The rules-based international order took off after World War II. After the conspicuous failure of World War I to stabilize Europe, the conscripts of that war, whose adulthood had been spent navigating the Great Depression, rose to strategic leadership positions in the Second World War. Their solution to world war and global depression was institution building on a global scale including the UN, the International Monetary Fund, NATO, and the predecessor institutions of the European Union (the European Economic Community) and the World Trade Organization (the General Agreement on Tariffs and Trade). They built strong institutions to create forums to hash out problems verbally rather than to fight them out militarily.

This emerging global order is fundamentally maritime because the oceans are the world’s original global network potentially connecting everyone to everything. In 2020, an article from the Center for International Maritime Security suggested a 66-70-80-90-99 rule highlighting that 66 percent of global wealth comes from or not far from the sea, 70 percent of the globe is oceanic, 80 percent of its population is coastal, 90 percent of goods arrive by sea, and 99 percent of digital traffic goes by submarine cable.1 This reflects the change in the currency of power from land to commerce. The incoming global maritime order focuses on compounding wealth by minimizing transaction costs, while the outgoing order of competing, wealth-destroying, continental empires focused on undermining each other. The old system destroyed wealth, the new one creates it.