Why did most European city walls get demolished by 1900 while many Asian city walls survived much longer?

Answer: Railways and factories made the land under European walls too valuable to keep

Railways and factories made the land under European walls too valuable to keep ✓ — 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 wall 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 their 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.