Iwatsuki castle no longer stands in Iwatsuki, because the castles represented the samurai. The Meiji government (1868-1912) desired to Westernize Japan and to update the country. Most of the samurai rebelled and fought against the changes, though ultimately losing. Since the castles held the rebellious groups, the Meiji government destroyed virtually all of the fortresses.
Inside those museums, the signs rarely emphasize one important detail. When the Meiji government took over, toppling the samurai and castles, they included freedom of religion within the constitution. The persecution of Christians ended with the Meiji government, allowing the name of Christ to spread once again.