In response to the national fraternity's segregationist membership policies, the fraternity went local in 1963, becoming Sigma Nu Delta. The national fraternity's policies were changed in <whatever year it happened>, and in 1984 the fraternity reaffiliated with the national.
Now we just need the fill in the blank.
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Because "undergrads, please abandon your national policies and make something up" will end well --KnightShadow