After the Union gained New Orleans, they could control the South of the Mississippi River
Britain gained Canada and east of Mississippi river except the City of New Orleans and two small islands.
Most of the produce of the interior states and territories floated on flatboats down the Mississippi to New Orleans for sale.
The Union gained control of the Mississippi river in the spring of 1862. The victory at Shiloh gave the North the advantage in the fight for control of the Mississippi River and the river valley.
I think you are asking about the Mississippi River and particularly the Gulf port of New Orleans. The US had free access to most of the River, but the Spanish and later the French controlled New Orleans and the port. The French gained control of New Orleans from Spain via a secret treaty on October 1, 1800.
The union gained control of the Mississippi after the capture of Vicksburg.
One direct result of the Battle o New Orleans was that the Union navy gained control over the entrance to the Mississippi River. The battle took place on January 8, 1815.
Think of the Mississippi as a highway and it can be used to ship goods and people. As well as have access to the Gulf of Mexico. This is vital for trade.
The Union gained complete control of the Mississippi River.
france
The United States gained the New Orleans seaport
Britain gained all of the French territories that were east of the Mississippi as a result of the war. They also gained portions of Canada.