Why did Switzerland stay out of both world wars?

Armed neutrality, recognised by the powers at the Congress of Vienna in 1815 and backed by a plan to make invasion expensive rather than impossible. Switzerland kept universal conscription and, in the Second World War, prepared the Reduit - a strategy of abandoning the plateau if invaded and holding the Alpine passes and tunnels from fortifications built into the mountains, while wiring those tunnels to be destroyed.

That threat was the point. The Alpine rail tunnels were the shortest route between Germany and Italy, and Switzerland made clear that an invasion would get the country without the tunnels. Combined with the cost of fighting in mountains, it made neutrality more valuable to Germany than conquest.

The neutrality has an uncomfortable ledger and Switzerland has spent decades examining it. Swiss banks handled looted gold; refugee policy turned Jewish refugees back at the border with the notorious formulation that the boat was full; and firms traded with both sides. A government-commissioned historical commission reported on all of it in the late 1990s and its findings were not comfortable reading. The country also only gave women the vote federally in 1971, and in one canton not until 1990, by order of the federal court.