Philip Bobbitt would argue that it was in large part different kinds of wars. The classic 20th C nation-state went hand-in-hand with 20th-C warfare: it needed

Philip Bobbitt would argue that it was in large part different kinds of wars. The classic 20th C nation-state went hand-in-hand with 20th-C warfare: it needed both massive industry, and every single man. The Ottomans and other relics of earlier times fell apart under the stress of such wars; the states that survived were those with a strong identity. Such identities were partly fostered for this very purpose. But we seem to have moved on from this, war is again a profession of a few (plus high-tech weapons), conscripting the millions would be of no use. And in parallel our ties to nations are weaker than before, both whether we'd fight for the flag & conversely whether the country is interested in safety nets etc. Our economy is also much less nation-based: GM in its heyday was quite unlike Apple. He calls this emerging form a "market state". Earlier forms also fought very different wars, he argues that Westphalia (and Waterloo) were among a series of such transitions, each entailing changes to what states are legitimate, and what kind of wars they fight. Anyway if this sounds interesting then his book "The Shield of Achilles" is cautiously recommended. Someone really needs to write a condensed version... but if you're willing to skip a bit, the ideas are great.