Complex sentence: The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups: one wanted to irrigate the ancient Grand Coulee with a gravity canal and the other supported a high dam and pumping scheme.
Split into simpler sentences: The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups. One wanted to irrigate the ancient Grand Coulee with a gravity canal and the other supported a high dam and pumping scheme.