which are the main tributaries of the missouri river?
James, Big Sioux, Grand River systems etc.
Missouri River
 Most rivers and streams in the Missouri River basin flow from west to east, following the incline of the Great Plains; however, some eastern tributaries such as the James, Big Sioux and Grand River systems flow from north to south.
what river forms the border between iowa and nebraska UNANSWERABLE
wiki:25677395
Missouri River [SEP] Major tributaries
Over 95 significant tributaries and hundreds of smaller ones feed the Missouri River, with most of the larger ones coming in as the river draws close to the mouth. Most rivers and streams in the Missouri River basin flow from west to east, following the incline of the Great Plains; however, some eastern tributaries such as the James, Big Sioux and Grand River systems flow from north to south. The Missouri's largest tributaries by runoff are the Yellowstone in Montana and Wyoming, the Platte in Wyoming, Colorado, and Nebraska, and the Kansas–Republican/Smoky Hill and Osage in Kansas and Missouri. Each of these tributaries drains an area greater than , and has an average discharge greater than .