Which two countries share the longest international border?

The longest international border between two countries is indeed shared by Canada and the United States. This border stretches for approximately 8,891 kilometers (or 5,525 miles), making it the longest continuous international boundary in the world. It runs from the Atlantic Ocean in the east to the Pacific Ocean in the west, including land and water boundaries.

Canada and the United States share a deep economic and cultural connection, and their border is characterized by several crossing points that facilitate trade and travel. The sheer length of this border reflects the vast land area that both countries encompass.

The other options do not have borders that compare in length to that of Canada and the United States. For instance, while Brazil and Argentina share a significant border, it is much shorter. Similarly, the border between India and China is extensive but does not surpass the Canada-U.S. border in length. The border shared between Canada and Mexico also doesn’t reach the same length as that between Canada and the United States.