Borders of the United States

Primary land borders

The two continuous international land borders are with Canada and Mexico. The Canada–United States border stretches across a broad northern frontier and is commonly described as the world's longest land border between two countries. To the south, the Mexico–United States border links the continental United States with Mexico and includes numerous official crossings, urban borderlands and rural stretches.

Characteristics and legal framework

Borders include clearly surveyed lines, natural features such as rivers and ridgelines, and maritime limits like territorial seas and exclusive economic zones. Their precise locations and governance rest on historical treaties, boundary commissions, bilateral protocols and domestic law. Crossings are regulated by customs and immigration authorities; some areas are remote while others accommodate heavy commercial traffic.

History and development

Current boundaries evolved over centuries through exploration, purchase and diplomacy. Key events influencing the lines include colonial-era agreements, the Treaty of Paris (1783), the Louisiana Purchase, the Oregon boundary settlement, the Treaty of Guadalupe Hidalgo and later survey work and compacts that refined lakeshore and river limits.

Uses, importance and contemporary issues

Borders are central to national sovereignty and everyday life: they support international trade corridors, shape cross-border communities, and require cooperation on security, public health and conservation. Contemporary challenges include migration management, infrastructure at ports of entry, cross-border pollution, and coordination on emergencies.

Notable facts and distinctions

• The northern border is renowned for its length and for extensive cooperative arrangements between neighbours.
• The southern border features varied landscapes—from urban megaregions to desert—and is a focus of migration and trade policy debates.
• Maritime boundaries and Great Lakes limits involve additional treaties and joint agencies to manage navigation, fishing and water quality.