Whoever controls that dam controls the entire southern portion of Iraq.
To give a comparison to events that occurred in the past, during the Japanese invasion of China in 1938, the Chinese destroyed dikes along the Yellow River in an effort to slow the Japanese. 1 million Chinese peasants died as a result. Some died fighting but the majority was due to flooding.
Threatens entire Tigris plain: could put Mosul under 100 feet of water, Baghdad 16 feet.