Complex sentence: In 1979, the DIA reported that the test may have been a Soviet test done in violation of the 1963 Partial Nuclear Test Ban Treaty,, the USSR had conducted a few secret underwater tests in the Pacific in 1959.
Split into simpler sentences: In 1979, the DIA reported that the test may have been a Soviet test done in violation of the 1963 Partial Nuclear Test Ban Treaty. The USSR had conducted a few secret underwater tests in the Pacific in 1959.