Nine out of ten of the world's most advanced chips are made on one island that almost no country will call a country.
Twelve governments recognize Taiwan, and the rest buy from it anyway, because almost half the world's container ships pass through the strait beside it.
In 1979 Washington switched its embassy from Taipei to Beijing, then passed a law promising weapons to Taiwan without ever promising rescue.
The line itself was improvised — an American general drew it down the middle of the strait in 1955, and both sides quietly obeyed.
It held for most of seven decades, until 2022, when Beijing said the line had never existed and started flying straight across it.
Last year Taiwan tracked more than five thousand Chinese military flights, over three thousand of them crossing the line that used to mean stop.
Taiwan's defense is made of silicon — one company builds most of the advanced chips that every army, bank and phone on earth runs on.
Break that, and Bloomberg's economists put the bill at ten trillion dollars in a single year, roughly one tenth of everything the world makes.
That number is the real fortification — not the missiles, not the treaties, but the fact that everyone's economy is standing on the same thin line.
But shields move — Taiwan's biggest chipmaker is now spending two hundred sixty-five billion dollars building those same factories in the Arizona desert.
Every factory built abroad shaves a little off the world's reason to intervene, so Taipei just approved twenty-five billion dollars in emergency weapons.
So the most protected island on earth is one almost nobody recognizes, guarded not by its allies but by the cost of losing it.