The way has been cleared for the first major railroad merger in more than two decades after federal regulators approved Canadian Pacific’s $31 billion acquisition of Kansas City Southern.

The two railroads are the nation’s two smallest, but the approval today by the U.S. Surface Transportation Board comes after a lengthy and arduous review because their coupling will create the only railroad linking Canada, Mexico and the United States.

The Transportation Board said that the new direct service “will facilitate the flow of grain from the Midwest to the Gulf Coast and Mexico, the movement of intermodal goods between Dallas and Chicago and the trade in automotive parts, finished vehicles, and other containerized mixed goods between the United States and Mexico.”

The board said the transaction, which will have little to no track redundancies or overlapping routes, is also expected to add more than 800 new union jobs in the U.S.