A common enemy war dissolved organized anti-immigrant nativism.

Evidence

The very heart of Know-Nothingism, the American party, vanished in 1860, its last surviving strength passing into the Constitutional Union party which stood for nothing but the preservation of the nation. … The war completed the ruin of organized nativism by absorbing xenophobes and immigrants in a common cause. Now the foreigner had a new prestige; he was a comrade-at-arms. The clash that alienated sections reconciled their component nationalities. — John Higham, Strangers in the Land, 79

Categorization

• XREF: Direct evidence for the reader’s central question: solidarity with a constructed external enemy (the Confederacy) displaced the manufactured Catholic/immigrant enemy, and organized nativism collapsed. — connects to: Immigration restrictions climaxed a wartime cascade of anti-foreign statutes — John Higham, Strangers in the Land: Patterns of…, 1806; Civil War nationalism displaced nativism by supplying shared enmity and economic bonds. — John Higham, Strangers in the Land: Patterns of…, 86; Civil War enlistment crushed prewar anti-immigrant nativism — John Higham, Strangers in the Land: Patterns of…, 77 (+5 more)

Broader Connections

• Civil War enlistment crushed prewar anti-immigrant nativism #corroborates (0.95) — John Higham, Strangers in the Land, 77
• Nativism can collapse even as the immigrant influx it fears soars #exemplifies (0.75) — John Higham, Strangers in the Land, 644