[TheCoelacanth]

Common sense was that Germans, Italians, Irish, etc. could never integrate into America.

Common sense was that Ocitanians and Bretons could never integrate into France.

Common sense was that hundreds of independent principalities with mutually unintelligible languages could never integrate into Germany and Italy.

Common sense was that Samnium and Lucanium could never integrate into Rome.

Except all of them did and those countries were stronger for it.