Story highlights Supreme Court held North Carolina illegally drew two congressional districts to pack them with African-American voters

Republicans control 10 US House seats; Democrats three

(CNN) The Supreme Court struck down two congressional district maps in North Carolina Monday, holding that the state had engaged in an unconstitutional racial gerrymander.

The ruling is a victory for the black North Carolina voters who had argued the plans packed African-Americans in districts that already had a high percentage of African-Americans, thus diluting their presence in other districts.

As a result, the ruling sends the North Carolina legislature back to the drawing board -- with significant potential implications for the 2018 midterm elections. The state has been nearly split along partisan lines in recent statewide elections -- such as for governor and president -- but Republicans control 10 US House seats compared to only three for Democrats.

"The Constitution entrusts states with the job of designing congressional districts," Justice Elena Kagan wrote for the majority. "But it also imposes an important constraint: A state may not use race as the predominant factor in drawing district lines unless it has a compelling reason."

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