Why did European city walls disappear by 1900 but not Asia's?

Answer: Railroads and industry made walls obsolete in Europe first

Railroads and industry made walls obsolete in Europe first ✓ — Correct! By 1850 European cities were exploding outward — railways, factories, suburbs all needed land that the wall blocked. Vienna tore down its walls in 1857, Cologne in 1881; the cleared rings became boulevards (Vienna's Ringstrasse). Asia's industrial transition came 50-100 years later, so most Asian walls survived longer — Beijing's wall stood until the 1950s, Xi'an's still stands today. The killer wasn't war; it was real estate.

Europeans ran out of stone for maintenance — Wrong. Europe had plenty of stone. Maintenance wasn't the problem — opportunity cost was. The land under the walls was suddenly more valuable as railway track and downtown real estate than as fortification.

Asian armies were stronger so walls were still needed — Wrong. By 1900 modern artillery had made ALL old walls useless against any real army. Asian walls survived because the local economic pressure to demolish came later, not because they retained military value.