The major tributary of the Mississippi River that flows in the southeasterly direction to join the Mississippi River near St. Louis is the Missouri River. The Missouri River and the Mississippi River join at the border between Missouri and Illinois.
The Missouri River is actually a major tributary to the Mississippi River, so the question does not make sense
The Arkansas River.
Arkansas river
The Missouri is a tributary of the Mississippi river. The Missouri is longest river at 2,500 miles. When the Missouri joins the Mississippi they become the largest river system in the world.
The Missouri joins the Mississippi near St. Louis, Missouri.
The Missouri river joins the Mississippi at St. Louis.
St Louis lies on the west bank of the Mississippi River. Just north of the city proper, the Missouri River joins the Mississippi.
missouri
The Missouri River joins the Mississippi very near St Louis.
St. louise river
The mighty Mississippi River has long been a valued source of commerce and food between Illinois and Missouri. With several tributaries feeding into it, the mightiest of those tributaries would have to be the mighty Missouri River which joins with the Mississippi North of St. Louis.
The Missouri River.